A to Z Terminology of surface treatment and heat treatment

 

            A to Z Terminology of surface treatment and heat treatment

Abradable coatings

Coatings which are designed to rub down against the action of a mating surface to form a tight gas or air seal.

Abrasion Resistance - Degree of resistance of a material to abrasion or wear.

Abrasive – A substance used for grinding, honing, lapping, superfinishing, polishing, pressure blasting or barrel finishing. It includes natural materials such as garnet, emery corundum and diamond and electric-furnace products like aluminum oxide, silicon carbide and boron carbide.

Abrasive blasting – A pressurized stream of hard metal or oxide grit material used to clean and / or roughen surfaces prior to coating.

Abrasive wear – Wear caused by hard, sharp particles.

Accm, Ac1, Ac3, and Ac4 – Defined under transformation temperature.

Acetylene C2H2 - Unsaturated aliphatic hydrocarbon gas. Used as a fuel gas in combustion thermal spray processes, welding and cutting. Acetylene has the highest flame temperature and requires the smallest amount of oxygen to form a neutral flame.

Acicular Ferrite – A highly sub-structured conequiaxed ferrite that forms upon continuous cooling by a mixed diffusion and shear mode of transformation that begins at a temperature slightly higher than the temperature transformation range for upper bainite. It is distinguished from bainite in that it has a limited amount of carbon available; thus, there is only a small amount of carbide present.

Acoustic emission – Acoustic emissions are sound or ultrasound pulses generated during crack initiation or propagation in materials and coatings as a result of being subjected to stress. Acoustic emissions can be detected by transducers.

Adhesion - The ability of a coating to remain on the surface without spalling, flaking or cracking. Adhesion is probably the single most important property of a coating.

Adhesion scratch test - Currently the most commonly used method of assessing coating adhesion. Used in the analysis of organic and inorganic soft and hard coatings. Examples are thin and multiplayer PVD, CVD, PECVD, TD, photoresist, paints, lacquers, and many other types of films, covering optical, micro-electronic, protective, decorative and other applications. Substrates can be hard or soft, including metals, alloys, semiconductors, glass, refractive and organic materials. Scratch testing consists of introducing stresses at the interface between coating and substrate. This is achieved by pressing a diamond stylus on the sample surface with a normal load FN. As the sample is displaced at constant speed, the resulting stresses at the interface cause flaking or chipping of the coating. The minimum load at which a specific failure event is recorded is call the Critical Load (Lc). See Critical Load.

Adhesive Wear - Wear caused by sliding surfaces, where surface asperities interact and adhere.

Aecm, Ae1, Ae3, and Ae4 – Defined under transformation temperature.

Aerated bath nitriding – A type of liquid nitriding in which air is pumped through the molten bath creating agitation and increased chemical activity.

Age hardening – Hardening by aging, usually after rapid cooling or cold working. See also aging.

Age softening – Spontaneous decrease of strength and hardness that takes place at room temperature in certain strain hardened alloys, especially those of aluminum.

Agglomerate - Several particles adhering together.

Agglomerated powder - A mechanically mixed combination of fine particles of different materials held together with an organic binder and formed into power particles.

Aging – A change in the properties of certain metals and alloys that occurs at ambient or moderately elevated temperatures after hot working or a heat treatment (quench aging in ferrous alloys, natural or artificial aging in ferrous and nonferrous alloys) or after cold working operation (strain aging). The change in properties is often, but not always, due to a chemical composition of the metal or alloy. See also age hardening, artificial aging, interrupted aging, natural aging, overaging, precipitation hardening, precipitation heat treatment, progressive aging, quench aging, step aging.

Air Cap - A component of thermal spray guns used for shaping the air flow for atomizing the wire or rod feedstock.

Air classification - The separation of powder into particle size fractions by means of an air stream of controlled velocity.

Air-hardening steel – steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range. The terms should be restricted to steels that are capable of being hardened by cooling in air in fairly large sections, about 2 in. (50 mm) or more in diameter. Same as self-hardening steel.

Alkyd resin - A type of polyester resin used in paints and other surface coating. The original alkyd resins were made by copolimerizing phathalic anhydride with glycerol, to give a brittle cross. Linked polymer.

Allotropy – A near synonym for polymorphism. Allotropy is generally restricted to describing polymorphic behavior in elements, terminal phases, and alloys whose behavior closely parallels that of the predominant constituent element.

Alloy – A substance having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

Alloying element – An element which is added to a metal (which remains within the metal) to effect changes in properties.

Alloy steel - Steel containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus) within the limits recognized for construction alloy steels, added to effect changes in mechanical or physical properties.

Alpha ferrite – See ferrite.

Alpha iron - The body-centered cubic form of pure iron, stable below 910°C (1670°F).

Alumina - Aluminum Oxide compound used in both abrasive blasting as an abrasive and in thermal spraying as a consumable feedstock (powder and rod) for the production of coatings. Alumina is a hard wear resistance ceramic and can be alloyed with various amounts of titania (titanium dioxide) to improve certain properties.

Aluminizing (gas) -- High temperature (approx 900°C) pack or gaseous diffusion of aluminum into the surface of a component to enhance high temperature corrosion and oxidation resistance.

Aluminizing (hot dip) - A liquid aluminum submersion technique at temperatures above 600°C depositing layer of aluminum (usually on steel sheet) for enhance corrosion protection

Aluminizing (thermal spray method) - Thermal sprayed coatings of aluminum usually on substrates of steel or nickel chromium alloys which are subsequently heat treated to aluminize the surface.

Aluminum (Al) – Used to deoxidize steel and control grain size. Grain size control is affected by forming a fine dispersion with nitrogen and oxygen which restricts austenite grain growth. Aluminum is also an extremely effective nitride former in nitriding steels.

Aluminum Ion Plating - The deposition of aluminum by a vacuum evaporative process. Provides galvanic corrosion resistance. Normally given a passivation treatment.

Amorphous - Non-crystalline, or devoid of regular structure.

Anion - A negatively charged ion.

Annealing – A generic term denoting a treatment, consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to: improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and/or increase in stability of dimensions. When the term is used without qualification, full annealing is implied. When applied only for the relief of stress, the process is properly called stress relieving or stress-relief annealing.
     In ferrous alloys, annealing usually is done above the upper critical temperature, but the time-temperature cycles vary widely in both maximum temperature attained and in cooling rate employed, depending on composition, material condition, and results desired. When applicable, the following commercial process names should be used: black annealing, blue annealing, box annealing, bright annealing, cycle annealing, flame annealing, full annealing, graphitizing, intercritical annealing, isothermal annealing, malleablizing, order hardening, process annealing, quench annealing, spheroidizing, subcritical annealing.
      In nonferrous alloys, annealing cycles are designed to: (a) remove part or all of the effects of cold working (recrystallization may or may not be involved); (b) cause substantially complete coalescence of precipitates from solid solution in relatively coarse form; or (c) both, depending on composition and material condition. Specific process names in commercial use are final annealing, full annealing, intermediate annealing, partial annealing, recrystallization annealing, stress-relief annealing, anneal to temper.

Annealing carbon - Fine, apparently amorphous carbon particles formed in white case iron and certain steels during prolonged annealing. Also called temper carbon.

Annealing twin - A twin formed in a crystal during recrystallization.

Anneal to temper - A final partial anneal that softens a cold worked nonferrous alloy to a specified level of hardness or tensile strength.

Anode – The positive electrode in a plasma spray torch (gun). Generally made from copper but can be lined with tungsten to increase life. See also cathode.

Anodic coating -A coating that becomes the anode in an electrochemical cell with the substrate (cathode). The only metals in common use for thermal spraying which are anodic to iron and steel are zinc and aluminum.

Anodizing - The production of an oxide layer on aluminum alloys. The process is electrolytic, a typical electrolyte being sulfuric acid. Treatment at room temperature produces thin, decorative layers with some corrosion protection. Treatment at 0°C produces hard, thicker layers (up to 100µ) with wear resistance. They can be post sealed to give improved corrosion resistance.

Antireflection coating (AR coating) - A coating whose reflection is zero, used for lenses. They are usually fabricated by the technique of interference oscillations with a He-Ne laser.

Apparent density - The weight of a unit volume of powder or coating

Apparent hardness – The value obtained by testing a coating or sintered material with standard indentation hardness equipment. See macro hardness. Since the reading reflects a composite of pores and solid material, (which may be particles relatively poorly bonded together) it is usually lower than that of an equivalent solid wrought or cast material. Not to be confused with particle hardness. See micro hardness.

Arcm, Ar1, Ar3, Ar4, Ar’, Ar” – Defined under transformation temperature.

Arc Blow (Plasma) - Arc blow is the deflection of an electric arc under the influence of the magnetic field associated to the flow of electrons (electric charge), which results in arc instability. Arc blow can be reduced and minimized in plasma welding by an appropriate design of shape and sizes of the electrodes (namely cathode tip and anodic nozzle plenum).

Arc Wire Spraying - A thermal spray process in which two electrically conducting wires are brought together to form an electric arc. The consequent molten metal is then projected by an air stream towards the work piece to form a coating.

Argon (Ar) - Monatomic noble gas, atomic number 18, one of the most inert elements. Commonly used as a plasma gas for plasma spraying and providing inert environments for many processes.

Artificial aging – Aging above room temperature. See aging. Compare with natural aging.

Athermal transformation – A reaction that proceeds without benefit of thermal fluctuations; that is, thermal activation is not required. In contrast, a reaction that occurs at constant temperature is an isothermal transformation; thermal activation is necessary in this case and the reaction proceeds as a function of time.

As cast - Referring to metal which has not received finishing (beyond gate removal or sandblasting) or treatment of any kind including heat treatment after casting. Similarly, as drawn, as forged and as rolled.

Atomization - The dispersion of a molten material into particles by a rapidly moving gas or liquid stream or by mechanical dispersion.

Atomic force microscopy (AFM) – An extremely accurate and versatile technique for measuring structures or surface forces. A very fine sensor tip mounted to the end of a small deflecting spring, known as a cantilever, is brought into contact with the sample surface to be investigated. The sensor tip is moved across the surface in numerous line scans. Due to the surface roughness (topography), the tip and the cantilever move up and down. This movement can be measured with high resolution and the resulting data allows imaging of the surface structure. Also called scanning probe microscopy.

Atomized powder - A powder produced by the dispersion of a molten material into particles by a rapidly moving gas or liquid stream or by mechanical dispersion.

Atmosphere - The gaseous environment in which the metal being treated is heated for processing. Atmospheres are used to protect from chemical change or to alter the surface chemistry of steel through the addition or removal of carbon, nitrogen, hydrogen, and oxygen and to add certain metallic elements as chromium, silicon, sulfur, etc.

Auger Electron Spectroscopy (AES) - An electron beam technique applied for near-surface elements identification. well used in thin film science.

Ausforming – Thermo mechanical treatment of steel in the metastable austenitic condition below the recrystallization temperature followed by quenching to obtain martensite and/or bainite.

Austempering – A heat treatment for ferrous alloys in which a part is quenched from the austenitizing temperature at a rate fast enough to avoid formation of ferrite or pearlite and then held at a temperature just above Ms until transformation to bainite is complete. Although designated as bainite in both austempered steel and austempered ductile iron (ADI), austempered steel consists of two phase mixtures containing ferrite and carbide, while austempered ductile iron consists of two phase mixtures containing ferrite and austenite.

Austenite – A solid solution of one or more elements in face-centered cubic iron. Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon.

Austenite Steel - Any steel containing sufficient alloy to produce a stable austenitic (gamma iron) crystalline structure at ambient temperatures.
Austenitic grain size – The size by the grains of steel when heated to the austenitic region; may be revealed by appropriate etching of cross sections after cooling to room temperature.

Austenitizing – Forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). When used without qualification, the term implies complete austenitizing.

Autoclaving - The production of a stable, protective oxide on steel parts by treatment in a pressurized, high temperature steam containing atmosphere.

---

B

Bainite – A metastable aggregate consisting of dispersed carbide in ferrite resulting from the transformation of austenite at temperatures below the pearlite range but above Ms. Its appearance is in the form of relatively coarse ferrite laths between which carbides are precipitated as platelets if formed in the upper part of the bainite transformation range; acicular, resembling tempered martensite, if formed in the lower part.

Bainitic hardening – Quench-hardening treatment resulting principally in the formation of bainite.

Banded structure - A layering effect that is sometimes developed during the hot rolling of steel.

Bark - An older term used to describe the decarburized skin that develops on steel bars heated in a non-protective atmosphere.

Base coats for electroplating - Materials that are difficult to electroplate because of rapid oxide formation can have an adherent base coat applied by PVD processes and then the coating built-up by electrodeposition. Examples are plating on titanium, uranium, and zirconium where a base coat of a material like nickel or copper is applied by a PVD process before the electroplated coating is built up.

Batch furnace – A furnace used to heat treat a single load at a time. Batch-type furnaces are necessary for large parts such as heavy forgings and are preferred for complex alloy grades requiring long cycles. See car furnace, horizontal batch furnace.

Belt furnace – A continuous-type furnace which uses a mesh-type or cast-link belt to carry parts through the furnace.

Beta annealing – Producing a beta phase by heating certain titanium alloys in the temperature range of which this phase forms followed by cooling at an appropriate rate to prevent its decomposition.

Billet - A solid semi finished round or square that has been hot worked usually smaller than a bloom. Also a general term for wrought starting stock for forgings or extrusions.

Binder - A cementing medium used in producing composite or agglomerate powders.

Black annealing – Box annealing or pot annealing ferrous alloy sheet, strip, or wire to impart a black color to the oxidized surface. See box annealing.

Black oxide – A black finish on a metal produced by immersing it in hot oxidizing salts or salt solutions.

Blackadizing - A pressurized stream of some materials (Glass, plastic, metal, ahs, etc) applied on a surface to clean and/or roughen. It can be, depending on the media, abrasive or non-abrasive.

Blank annealing – Simulating the carburizing operation without introducing carbon. This is usually accomplished by using an inert material in place of the carburizing agent, or by applying a suitable protective coating to the ferrous alloy.

Blank Carburizing - Simulating the caruburizing operation without introducing carbon. This is usually accomplished by using an inert material in place of the carburizing agent, or by applying a suitable protective coating to the ferrous alloy.

Blank nitriding – Simulating the nitriding operation without introducing nitrogen. This is usually accomplished by using an inert material in place of the nitriding agent or by applying a suitable protective coating to the ferrous alloy.

Blasting - A pressurized stream of particulates (ceramic, plastic, metal, etc.) applied on a surface to clean, peen or abrade.

Blended Powder - A powder consisting of two or more different powder materials thoroughly mixed.

Bloom - A semi-finished hot rolled rectangular product. The width of the bloom is no more than twice the thickness and the cross-sectional area is usually not less that 36 square inches.

Blue annealing – Heating hot-rolled ferrous steel in an open furnace to a temperature within the transformation range and then cooling in air, in order to soften the metal. The formation of a bluish oxide on the surface is incidental.

Blue brittleness – Brittleness exhibited by some steels after being heated to some temperature within the range of about 205 to 370°C (400 to 700°F), particularly if the steel is worked at the elevated temperature. Killed steels are virtually free of this kind of brittleness.

Bluing – Subjecting the scale-free surface of a ferrous alloy to the action of air, steam, or other agents at a suitable temperature, thus forming a thin blue film of oxide and improving the appearance and resistance to corrosion. Note: This term is ordinarily applied to sheet, strip, or finished parts. It is used also to denote the heating of springs after fabrication to improve their properties.

Bond - This represents the state of adhesion between the coating and the substrate. Its strength will depend on the details of the thermal spraying process and the materials used. Bonding mechanisms may be mechanical, physical or metallurgical or a combination of these.

Bond coat - A coating applied as an intermediary between the main or top coating and the substrate in order to improve the bond strength.

Bond strength - The strength of the adhesion between the coating and the substrate. A number of test methods are in use to measure the bond strength of coatings.

Boriding – Thermo chemical treatment involving the enrichment of the surface layer of an object with borides. This surface-hardening process is performed below the Ac1 temperature.

Boron (B) - is usually added between .0005-.003% to significantly increase the hardenability, especially for low carbon alloys. It does not affect the strength of ferrite, therefore not sacrificing ductility, formability or machinability in the annealed state.

Boronizing - The diffusion of boron into the surface of a component (usually steel) by a high temperature (approx. 900°C) gas or pack process. Produces hard phases within the surface (Typically 100µm deep).

Boundary condition - The loads, displacements, temperatures, densities etc. at the periphery of the domain or mesh in a numerical simulation.

Box annealing – Annealing a metal or alloy in a sealed container under conditions that minimize oxidation. In box annealing a ferrous alloy, the charge is usually heated slowly to a temperature below the transformation range, but sometimes above or within it, and is then cooled slowly; this process is also called close annealing or pat annealing. See black annealing.

Breaks – Creases or ridges usually in “untempered” or in aged material where the yield point has been exceeded. Depending on the origin of the break, it may be termed a cross break, a coil break, an edge break, or a sticker break.

Bright annealing – Annealing in a protective medium to prevent discoloration of the bright surface. Compare with blank nitriding.

Brinell hardness test – A test for determining the hardness of a material for forcing a hard steel or carbide ball of specified diameter into it under a specified load. The result is expressed as the Brinell hardness number, which is the value obtained by dividing the applied load in kilograms by the surface area of the resulting impression in square millimeters.

Brine quenching – A quench in which brine (salt water-chlorides, carbonates, and cyanides) is the quenching medium. The salt addition improves the efficiency of water at the vapor phase or hot stage of the quenching process.

Brittle fracture – Separation of a solid accompanied by little or no macroscopic plastic deformation. Typically, brittle fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture.

Brittle tempering range - Some hardened steels show an increase in brittleness when tempered in the range of about 450°F to 700°F even though some tempering causes some softening.

Burning – (1) Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See overheating, grain-boundary liquidation. (2) In grinding, getting the work hot enough to cause discoloration or to change the microstructure by tempering or hardening.

 

Cadmium ion plating - The deposition of cadmium by a vacuum process to provide galvanic corrosion protection.

Cadmium plating - The electrolytic deposition of cadmium to provide galvanic corrosion protection. Restricted by environmental considerations.

Calcium (Ca) - is used in certain steels to control the shape, size and distribution of oxide and/or sulfide inclusions. Benefits may include improved ductility, impact strength and machinability.

Calorizing – Imparting resistance to oxidation to an iron or steel surface by heating in aluminum powder at 800 to 1000°C (1470 to 1830°F).

Capped steel - A type of steel similar to rimmed steel, usually cast in a bottle top ingot, in which the application of a mechanical or chemical cap renders the rimming action incomplete by causing the top metal to solidify.

Carbon (C) - is the most important alloying element which is essential for the formation of cementite, pearlite, spheriodite, bainite, and iron-carbon martensite. Compared to steels with similar microstructures, strength, hardness, hardenability, and ductile-to-brittle transition temperature are increased with increasing carbon content up to approximately .60%. Toughness and ductility of pearlitic steels are decreased with increasing carbon content.

Carbonitriding – A case hardening process in which a suitable ferrous material is heated (about 900°C by pack, gas, salt bath or plasma process) above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the desired properties in the workplace. Compare to carburizing.

Carbonization – Conversion of an organic substance into elemental carbon. (Should not be confused with carburization.)

Carbon potential – A measure of the stability of an environment containing active carbon to alter or maintain, under prescribed conditions, the carbon level of the steel. Note: In any particular environment, the carbon level attained will depend on such factors as temperature, time, and steel composition.

Carbon restoration – Replacing the carbon lost in the surface layer from previous processing by carburizing this layer to substantially the original carbon level. Sometimes called recarburizing.

Carbon steel – Steel having no specified minimum quantity for any alloying element (other than the commonly accepted amounts of manganese, silicon, and copper) and containing only an incidental amount of any element other than carbon, silicon, manganese, copper, sulfur, and phosphorus.

Carburizing – Absorption and diffusion of carbon into solid ferrous alloys by heating (about 900°C by pack, gas, salt bath or plasma process), to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperatures or by cooling to room temperature, then reaustenitizing and quenching.

Carburizing flame – A gas flame that will introduce carbon into some heated metals, as during a gas welding operation. A carburizing flame is a reducing flame, but a reducing flame is not necessarily a carburizing flame.

Car furnace – A batch-type furnace using a car on rails to enter and leave the furnace area. Car furnaces are used for lower stress relieving ranges.

Carrier gas – Usually nitrogen or argon gas that carries powder into the thermal spray process.

Case – That portion of a ferrous alloy, extending inward from the surface, whose composition has been altered so that it can be case hardened. Typically considered to be the portion of the alloy (a) whose composition has been measurably altered from the original composition, (b) that appears dark on an etched cross section, or (c) that has hardness, after hardening, equal to or greater than a specified value. Contrast with core.

Case-Depth – The hardened depth on carburized or nitrided parts, often defined as the depth to which the hardness exceeds 500 Hv.

Case hardening – A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The processes commonly used are carburizing and quench hardening; cyaniding; nitriding; and carbonitriding. The use of the applicable specific process name is preferred.

Casting – (1) An object at or near finished shape obtained by solidification of a substance in a mold. (2) Pouring molten metal into a mold to produce an object of desired shape.

Cathode – The negative electrode in a plasma torch (gun). Generally made from thoriated tungsten (thorium is added to reduce the metal work function aiding electron release). See also anode.

Cathodic coating – Coatings which become the cathode in an electrochemical cell with the substrate (anode). This type of coating protects the substrate from corrosion only by being a complete barrier. If the coating allows the environment to reach the substrate, accelerated corrosion of the substrate will occur.

Cathodic protection – A technique to reduce the corrosion rate of a metal by making it the cathode of an electrochemical cell. Thermal spray zinc and aluminum coatings provide this protection to steel substrates, the coating being the anode and the steel being the cathode.

Cation - A positively charged ion.

Caustic quenching – Quenching with aqueous solutions of 5 to 10% sodium hydroxide (NaOH).

Cavitation – The formation and rapid collapse within a liquid of cavities or bubbles that contain vapor or gas or both.

Cavitation erosion – A form of erosion causing material to be removed by the action of vapor bubbles in a very turbulent liquid.

CCT diagram – See continuous cooling transformation diagram.

Cermet powders – A composite powder of metal and ceramic constituents produced by methods such as agglomeration, sintering and spray drying. Examples include WC-Co, TiC-Ni.

Cementation – The introduction of one or more elements into the outer portion of a metal object by means of diffusion at high temperature.

Cementite – A compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements.

CFD – An acronym for Computational Fluid Dynamics

Checks – Numerous, very fine cracks in a coating or at the surface of a metal part. Checks may appear during processing or during service and are most often associated with thermal treatment or thermal cycling. Also called check marks, checking, heat checks.

Chemical conversion coating – A protective or decorative nonmetallic coating produced by chemical reaction of a metal with a chosen environment. (It is often used to prepare the surface prior to the application of an organic coating.)

Chemical Vapor Deposition (CVD) – The deposition of a coating by means of a chemical reaction in gases in a chamber producing components which deposit on and adhere to the substrate.

Chromating – Chromate conversion is a process which completely degreases and removes all traces of the oxide film, replacing it by immersion with a chromate coating which can then be painted. It is used as a post-treatment for cadmium, zinc and aluminum coatings

Chromic acid anodizing – A gray/brown anodic coating (1-2 micron) produced on Aluminum Alloys in Chromic acid at room temperature. It will act as an effective undercoat for paint.

Chromizing – High temperature (approx 900°C) pack or gaseous diffusion of chromium into the surface of a component to enhance high temperature corrosion and oxidation resistance.

Chromium (Cr) – is used in low alloy steels to increase 1) resistance to corrosion and oxidation, 2) high temperature strength, 3) hardenability, and 4) abrasion resistance in high carbon alloys. Straight chromium steels are susceptible to temper embrittlement and can be brittle.

Chromium Nitride – Metallic colored ceramic, often applied as a thin coating by PVD. Very hard (3500Hv). Used on cutting tools and other surfaces needing wear resistance.

Cladding - The application of a thick (generally above 1mm) coating which melts or diffuses into the substrate. Processes include weld cladding and plasma transferred arc (PTA).

Close annealing – Same as box annealing.

Coalescence – Growth of grains at the expense of the remainder by absorption or the growth of a phase or particle at the expense of the remainder by absorption or reprecipitation.

Coating - The application of a thin (generally less than 1mm) layer of material onto the surface of a substrate.

Coating thickness – Optical inspection of the depression reveals the projected surfaces of the abraded coating and substrate sections. By measuring the parameters X and Y, the thickness of the coating can be calculated by a simple geometrical equation.

Coating wear – Wear can be determined by using a slurry composed of water and SiC particles falling continuously onto the ball at the contact region. The slurry wears the substrate in a controlled manner and thus assures highly reproducible results. By comparing the geometry of the crater for different periods of wear time, the wear rate of the coating and the substrate can be determined precisely.

Coatings, corrosion protective - Protection from an aggressive chemical environment can be accomplished in several ways. The surface can be coated with an inert material or with a material that forms a protective surface after reacting with the environment or with a material that will be sacrificially removed to protect the underlying material. Tantalum, platinum, and carbon are inert in many chemical environments. For example, carbon coatings are used on metals that are implanted in the human body to provide compatibility. In the aerospace industry parts are aluminum coated by the PVD process of ion vapor deposition (IVD) so as to prevent galvanic corrosion of dissimilar materials in contact. Chromium, aluminum, silicon, and the MCrAlY (where M is Ni, Co, Fe) alloys will react with oxygen to form a coherent protective oxide layer on the surface. If the metal ions (Fe, Cu) diffuse more rapidly than the oxygen through the oxide, a thick oxide will form on the surface. If the oxygen diffuses more rapidly through the oxide than the metal ions (Al, Si, Ti, Zr—the "valve" metals), oxidation will occur at the interface and a thin oxide will be formed. The MCrAlY alloy coatings are used as protective coatings on aircraft engine turbine blades. Cadmium, aluminum, and Al:Zn alloys are used as galvanic sacrificial coatings on steel. Vacuum cadmium ("vac cad") plating has the advantage over electroplated cadmium in that there is no possibility of hydrogen embrittlement of high-strength steel when vacuum deposition processing is used.

Coatings, decorative and decorative/wear - Metallization for strictly decorative purposes is a large market. Applications vary from coating polymer webs—which are then converted to decorative uses such as balloons and labels—to metallization of three-dimensional articles, such as sports trophies, zinc die cast and molded polymer decorative fixtures, and cosmetic containers. Often these coatings consist of a reflective aluminum coating that is deposited on a smooth base coat, then over coated with a dyed lacquer to give the coating the desired color and texture and also corrosion and wear resistance. In some applications, in addition to the decorative aspects of the coating, the coating is required to withstand wear. For example, titanium nitride (TiN) is gold colored, and titanium carbonitride (TiCxNy) can vary in color from gold to purple to black depending on the composition. Zirconium nitride (ZrN) has the color of brass and is much more wear and scratch resistant than brass. Decorative/wear coatings are used on door hardware, plumbing fixtures, fashion items, marine hardware, and other such applications.

Coatings, hard and wear-resistant - Hard coatings are often called metallurgical coatings and are a type of tribological coating. The hard coatings are used to increase the cutting efficiency and operational life of cutting tools and to maintain the dimensional tolerances of components used in applications where wear can occur, such as injection molds. In addition, the coatings can act as a diffusion barrier where high temperatures are generated by motion between surfaces or corrosion protection in aggressive environments. There are various classes of hard coating materials. They include: ionically bonded metal oxides (Al2O3, ZrO2, and TiO2), covalently bonded materials (SiC, boron carbon [B4C], diamond, diamond-like-carbon [DLC], TiC, AlN, CrC, mixed carbide, vanadium carbide, nitride and carbonitride compound alloys, and cubic boron nitride), and some metal alloys (cobalt chromium aluminum yttrium [CoCrAlY], NiAl, NiCrBSi). In some cases the coatings may be layered to combine properties. Hard coatings also are used to minimize fatigue-wear, such as is found in ball bearings. Wear-resistant coatings also may be applied to surfaces where there is a light or periodic load. For example, hard coatings are deposited on plastics to improve scratch resistance. Applications are on molded plastic lenses and plastic airplane canopies. In some cases wear coatings, such as SiO2 or Al2O3, may be applied to already hard surfaces, such as glass, to increase the scratch resistance.

Coatings, packaging - Barrier coatings are used on flexible polymer films and paper for food packaging to reduce the water vapor transmission rate (WVTR) and the oxygen transmission rate (OTR) through the paper or polymer film. The most common barrier coating material is aluminum, which is deposited on rolls of polymer film (web), then supplied to "converters" who fabricate the packaging. In some cases the metal coatings are deposited on a surface and then "transferred" to the packaging film. Transparent barrier coatings are desirable in many instances. Layers of SiO2-x, by reactive evaporation and PECVD and composite coatings of SiO2:30% Al2O3 by E-beam co-evaporation are used to form transparent barrier layers. The composite coating material is more dense and flexible than the SiO2 or Al2O3 deposited material alone. Aluminum films are used on polymer helium-filled balloons to reduce the loss of helium

Coatings, reflector - Metal films are widely used for reflector surfaces. Silver is often used when corrosion is not a problem, such as for back-surface mirrors. Aluminum can be used either as a front-surface or back-surface reflector. Often, aluminized front-surface reflectors, such as headlight reflectors, are over coated with a protective polymer film (top coat). Chromium is used on front-surface reflectors when corrosion is a problem even though its reflectivity in the visible (60%) is less than that of aluminum (> 90%). Reflector films are used in numerous commonly encountered applications, such as on compact discs for video and music storage, lamp reflectors, and visual mirrors such as the rear-view mirrors for cars. In some cases multilayer films, similar to multilayer optical films, are used to selectively reflect certain wavelengths and not others. Examples are "cold mirrors" that reflect the visible radiation but not the infrared wavelengths and "heat mirrors" that reflect the infrared but not the visible. Heat mirrors are used to raise the internal temperature of halogen lamps. Cold mirrors are used to reduce the heat of stage lighting on actors.

Coatings, solid film lubricants/low friction - NASA pioneered the use of vacuum-deposited thin film solid lubricants. The lubricants are of two types: the low-shear metal lubricants—such as silver and lead—and the laminar-shearing compound materials—such as molybdenum disulfide (MoS2). The low-shear metal lubricants are used in high-torque applications such as the rotating anodes in X-ray tubes. Low-shear compound materials are used in mechanical-bearing applications in vacuum and where lubricant "creep" can be a problem. Because only a very thin film is needed for lubrication, the application of the lubricant film does not result in significant changes of dimensions. Low friction coatings of metal-containing carbon (Me-C) are used to reduce wear in mechanical contact applications.

Coatings, thermal control - The composition of the thermal control coatings on windows differs with the end result desired. If the object is to keep solar radiation from entering through the window, a multilayer film of glass-TiO2-Cr-TiO2 may be used (solar control coating). If the object is to keep heat in the room, a thin film of silver can be used to reflect 85% to 95% of the low-temperature infrared radiation back into the room (low-E coating). One such "double-E coating" is glass-ZnO-Ag-(Ti)-ZnO-Ag-(Ti)-ZnO-TiO2. The ZnO provides an antireflective coating. Other types of thermal control coatings are used to absorb solar radiation (solar absorbers), selectively adsorb solar radiation and not emit infrared radiation (selective solar absorbers), or to have a high emissivity to enhance cooling by radiation. Thermal barrier coatings are used to reduce the thermal transport from a hot environment to the substrate. Zirconium oxide (ZrO2) stabilized with calcium oxide (CaO), MgO, or Y2O3 is used as a thermal barrier coating on aircraft engine turbine blades.

Coarsening – An increase in the grain size, usually, but not necessarily, by grain growth.

Coherent precipitate – A crystalline precipitate that forms from solid solution with an orientation that maintains continuity between the crystal lattice of the precipitate and the lattice of the matrix, usually accompanied by some strain in both lattices. Because the lattices fit at the interface between precipitate and matrix, there is no discernible phase boundary.

Cold die quenching – A quench utilizing cold, flat, or shaped dies to extract heat from a part. Cold die quenching is slow, expensive, and is limited to smaller parts with large surface areas.

Cold dry die quenching – Same as cold die quenching.

Cold treatment – Treatment carried out after quenching to transform retained austenite into martensite, involving cooling and holding at a temperature below ambient.

Cold welding - Cohesion between two surfaces of a metal, generally under the influence of externally applied pressure at room temperature.

Cold working - Plastic deformation of a metal at a temperature low enough so that re-crystallization does not occur during cooling.

Columnar structure – A coarse structure of parallel elongated grains formed by unidirectional growth, most often observed in castings, but sometimes in structures resulting from diffusional growth accompanied by a solid-state transformation.

Combined carbon – The part of the total carbon in steel or cast iron that is present as other than free carbon.

Composite - Mixture of two or more materials. Nearly all have a reinforcing material (wood, glass, etc), called filler, and a natural or artificial resin, called matrix to achieve specific characteristics and required properties.

Composite Coating - Mixture of two or more materials. Many thermal spray coatings could be considered as composites.

Composite Powder - A powder in which each particle consists of two or more distinct materials joined together. (Not the same as a powder blend.)

Compound layer - A non-etching layer of iron nitrides formed at the surface of ferrous materials during nitriding or nitrocarburizing. Normally removed by grinding prior to component installation

Computational Fluid Dynamics (CFD) - A method of simulating a flow field on a computer, by replacing the governing nonlinear partial differential equations (Navier-Stokes Equations) with numbers, and advancing these numbers in space/time to obtain a final numerical description of the flow.

Conditioning heat treatment – A preliminary heat treatment used to prepare a material for desired reaction to a subsequent heat treatment. For the term to be meaningful, the exact heat treatment must be specified.

Congruent transformation – An isothermal or isobaric phase change in which both of the phases concerned have the same composition throughout the process.

Constitution diagram – See phase diagram.

Constricted arc (Plasma) - Column of plasma arc obtained by a constricted nozzle (usually in Copper and water cooled) connected to positive polarity (anode), while the negative polarity is connected to the cathodic electrode (usually tungsten added with thorium oxides).

Continuous Casting - Operation in which a cast shape is continuously drawn through the bottom of the mold as it solidifies. The length is not determined by mold dimensions.

Continuous cooling transformation (CCT) diagram – Set of curves drawn using logarithmic time and linear temperature as coordinates, which define for each cooling curve the beginning and end of the transformation of the initial phase.

Continuous precipitation – Precipitation from a supersaturated solid solution in which the precipitate particles grow by long-range diffusion without recrystallization of the matrix. Continuous precipitates grow from nuclei distributed more or less uniformly throughout the matrix. They usually are randomly oriented, but may form a Widmanstätten structure. Also called general precipitation. Compare with discontinuous precipitation, localized precipitation.

Continuous-type furnace – A furnace used for heat treating materials that progress continuously through the furnace, entering one door and being discharged from another. See belt furnace, direct-fired tunnel-type furnace, rotary retort furnace, shaker-hearth furnace.

Controlled cooling – Cooling from an elevated temperature in a predetermined manner, to avoid hardening, cracking, or internal damage, or to produce desired microstructure or mechanical properties.

Convergence - A description of the decrease in the relative error between successive iterations in a numerical solution. When a certain predefined limited has been reached, the solution is considered to have converged, and therefore the solution is stable and correct.

Cooling curve – A curve showing the relation between time and temperature during the cooling of a material.

Cooling stresses – Residual stresses resulting from non-uniform distribution of temperature during cooling.

Copper (Cu) - is detrimental to hot workability and subsequent surface quality. It is used in certain steels to improve resistance to atmospheric corrosion. For foundry applications, copper is meant to include all alloys containing 98% or more copper. Used for conductivity castings. Melting point 1083°C (1981.4°F).

Copper plating - The electrolytic deposition of copper to provide either a corrosion barrier (often as an undercoat for hard chrome plate) or for reclamation of worn parts.

Core – In a ferrous alloy prepared for case hardening, that portion of the alloy that is not part of the case. Typically considered to be the portion that (a) appears light on an etched cross section, (b) has an essentially unaltered chemical composition, or (c) has a hardness, after hardening, less than a specified value.

Corrosion – (1) Gradual chemical or electrochemical attack on a metal by atmosphere, moisture or other agents. (2) Chemical attack of furnace linings by gases, slags, ashes or other fluxes occurring in various melting practices.

Corrosion fatigue - The process in which a metal fractures prematurely under conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or fewer cycles than would be required in the absence of the corrosive environment.

Corrosion Index - A number expressing the maximum depth in microns or mils to which corrosion would penetrate in one year on the basis of a linear extrapolation of the penetration occurring during the lifetime of a given test or service.

Corrosion potential - The potential of a corroding surface in an electrolyte relative to a reference electrode measured under open circuit conditions.

Corrosive wear - Wear in which chemical or electrochemical reaction with the environment is significant.

Cr-Ni coatings - Anticorrosion coatings resistant to high temperatures.

Cracking - Breaks or splits in the coating's surface

Cracking Strip - A fin of metal molded on the surface of a casting to prevent cracking.

Crevice corrosion - Localized corrosion of a metal surface at, or immediately adjacent to, an area that is shielded from the full exposure to the environment because of close proximity between the metal and the surface of another material.

Critical cooling rate – The rate of continuous cooling required to prevent undesirable transformation. For steel, it is the minimum rate at which austenite must be continuously cooled to suppress transformations above Ms temperature.

Critical diameter (D) – Diameter of the bar that can be fully hardened with 50% martensite at its center.

Critical Load (Lc) – The Critical Load value translates the complex intrinsic properties of a specific coating system into very reproducible figures of great practical significance. Scratch testers provide cross-referenced data on Lc by simultaneously recording three different effects: tangential force variations, acoustic emission fluctuations, and microscopic deformations.

Critical point – (1) The temperature or pressure at which a change in crystal structure, phase, or physical properties occurs. Same as transformation temperature. (2) In an equilibrium diagram, that specific value of composition, temperature, and pressure, or combination thereof, at which the phases of a heterogeneous system are in equilibrium.

Critical range - The temperature range between an upper and lower critical point for a given material.

Critical strain – The strain just sufficient to cause recrystallization; because the strain is small, usually only a few percent, recrystallization takes place from only a few nuclei, which produces a recrystallized structure consisting of very large grains.

Critical temperature – (1) Synonymous with critical point if the pressure is constant. (2) The temperature above which the vapor phase cannot be condensed to liquid by an increase in pressure.

Critical temperature ranges – Synonymous with transformation ranges, which is the preferred term.

Crushed powder - Powder formed from a solid which is then crushed to the appropriate size for spraying.

Cryogenic treatment – See cold treatment.

Curie temperature – The temperature of magnetic transformation below which a metal or alloy is ferromagnetic and above which is paramagnetic.

CVD - See Chemical Vapor Deposition

Cyaniding – A case-hardening process in which a ferrous material is heated above the lower transformation range in a molten salt containing cyanide to cause simultaneous absorption of carbon and nitrogen at the surface and, by diffusion, create a concentration gradient. Quench hardening completes the process.

Cycle annealing – An annealing process employing a predetermined and closely controlled time-temperature cycle to produce specific properties or microstructures.

---

D

Dead soft – A temper of nonferrous alloys and some ferrous alloys corresponding to the condition of minimum hardness and tensile strength produced by full annealing.

Degreasing - The removal of grease and oil from a surface. Degreasing by immersion in liquid organic solvents or by solvent vapors condensing on the parts to be cleaned.

Decalescence – A phenomenon, associated with the transformation of alpha iron to gamma iron on the heating (superheating) of iron and steel, revealed by the darkening of the metal surface owing to the sudden decrease in temperature caused by the fast absorption of the latent heat of transformation. Contrast with recalescence.

Decarburization – Loss of carbon from the surface layer of a carbon-containing alloy due to reaction with one or more chemical substances in a medium that contacts the surface.

Degreasing - The removal of grease and oil from a surface. Degreasing by immersion in liquid organic solvents or by solvent vapors condensing on the parts to be cleaned.

Degrees of freedom – The number of independent variables (such as temperature, pressure, or concentration within the phases present) that may be altered at will without causing a phase change in an alloy system at equilibrium; or the number of such variables that must be fixed arbitrarily to define the system completely.

Delta ferrite – See ferrite.

Density - The mass per unit volume of a substance, usually expressed in grams per cubic centimeter or in pounds per cubic foot.

Deposit corrosion - Localized corrosion under or around a deposit or collection of material on a metal surface. See also crevice corrosion.

Detonation Gun - A thermal spraying process in which the coating material is heated and accelerated to the work piece by shock waves from a series of detonations or explosions from gas mixtures. Also known as D-Gun (Praxair).

Dew point – The temperature and pressure at which a gas begins to condense to a liquid.

Dew point analyzer – An atmosphere monitoring device that measures the partial pressure of water vapor in an atmosphere.

DI (Ideal Diameter) - The diameter of a round steel bar that will harden at the center to a given percent of martensite when subjected to an ideal quench (i.e., Grossman quench severity H=infinity)

Diamond Like Carbon - A thin film coating applied by a PVD or CVD process. It possesses some of the hardness of diamond, but with the low friction properties of graphite (Friction Coefficient = about 0.1). Used on cutting and forming tools, on medical implants and for low friction surfaces.

Die - A metal block used in forming materials by casting, molding, stamping, threading, or extruding.

Die Assembly - The parts of a die stamp or press that hold the die and locate it for the punches.

Die Casting - A rapid, water-cooled permanent mold casting process limited to nonferrous metals. There are three types: the plunger-type operated hydraulically, mechanically or by compressed air with or without a gooseneck; the direct-air injection which forces metal from a goose-neck into the die, and the Cold-Chamber Machine. All force the metal into the die with a pressure greater than that of gravity flow.

Die Coating - A material, e.g. silicone, stearate, oil, or wax for lubricating a die pattern or core box to facilitate easy removal of a casting, mold or core.

Differential heating – Heating that intentionally produces a temperature gradient within an object such that, after cooling, a desired stress distribution or variation in properties is present within the object.

Diffusion – (1) Spreading of a constituent in a gas, liquid, or solid, tending to make the composition of all parts uniform. (2) The spontaneous movement of atoms or molecules to new sites within a material.

Diffusion coefficient – A factor of proportionality representing the amount of substance diffusing across a unit area through a unit concentration gradient in unit time.

Dilatometer – An instrument for measuring the linear expansion or contraction in a metal resulting from changes in such factors such as temperature and allotropy.

Dip Coat - In solid and shell mold investment casting, a fine ceramic coating applied as a slurry to the pattern to produce maximum surface smoothness, followed by a cheaper conventional investment.

Direct Chill (DC) Casting - A continuous method of making ingots or billets or extrusion by pouring the metal into a short mold. Some times called semi-continuous casting.

Direct-fired tunnel-type furnace – A continuous-type furnace where the work is conveyed through a tunnel-type heating zone, and the parts are hung on hooks or fixtures to minimize distortion.

Direct quenching – (1) Quenching carburized parts directly from the carburizing operation. (2) Also used for quenching pearlitic malleable parts directly from the malleablizing operation.

Dirty Casting - A casting containing an excessive amount of nonmetallic inclusions in the body of the metal.

Discontinuous precipitation – Precipitation from a supersaturated solid solution in which the precipitate particles grow by short-range diffusion, accompanied by recrystallization of the matrix in the region of precipitation. Discontinuous precipitates grow into the matrix from nuclei near grain boundaries, forming cells of alternate lamellae of precipitate and depleted (and recrystallized) matrix. Often referred to as cellular or nodular precipitation. Compare with continuous precipitation, localized precipitation.

Dissociation – As applied to heterogeneous equilibria, the transformation of one phase into two or more new phases of different composition. Compare with order-disorder transformation.

Disturbed Metal - The cold worked metal formed on a polished surface during the processes of grinding and polishing.

Double aging – Employment of two different aging treatments to control the type of precipitate formed from a supersaturated matrix in order to obtain the desired properties. The first aging treatment, sometimes referred to as intermediate or stabilizing, is usually carried out at higher temperature than the second.

Double tempering – A treatment in which a quench-hardened ferrous metal is subjected to two complete tempering cycles, usually at substantially the same temperature, for the purpose of ensuring completion of the tempering reaction and promoting stability of the resulting microstructure.

Drawing – A misnomer for tempering.

Dry cyaniding – (obsolete) Same as carbonitriding.

Dry Sand Casting - The process in which the sand molds are dried at above 100°C (212°F) before using.

Ductile cast iron – A cast iron that has been treated while molten with an element such as magnesium or cerium to induce the formation of free graphite as nodules or spherulites, which imparts a measurable degree of ductility to the cast metal. Also known as nodular cast iron, spherulitic graphite cast iron, and SG iron.

Ductile fracture – Fracture characterized by tearing of metal accompanied by appreciable gross plastic deformation and expenditure of considerable energy. Contrast with brittle fracture.

Ductility – The ability of a material to deform plastically without fracturing, measured by elongation or reduction of area in a tensile test, by height of cupping in an Erichsen test, or by other means.

Dust - Small solid particles created by the breaking up of larger particles.

475°C (885°F) embrittlement – Embrittlement of stainless steels upon extended exposure to temperatures between 400 and 510°C (750 and 950°F). This type of embrittlement is caused by fine, chromium-rich precipitates that segregate at grain boundaries; time at temperature directly influences the amount of segregation. Grain-boundary segregation of the chromium-rich precipitates increases strength and hardness, decreases ductility and toughness, and changes corrosion resistance. This type of embrittlement can be reversed by heating above the precipitation range.

 

Elastic limit – The maximum stress that a material is capable of sustaining without any permanent strain (deformation) remaining upon complete release of the stress.

Elastic modulus (also called Young's modulus) - A parameter which measures the stiffness of a material.

Elasticity - The property of certain materials that enables them to return to their original dimensions after an applied stress.

Electrical Insulators - Electrically insulating films are used to electrically isolate conducting components in semiconductor devices, and as a dielectric within capacitors. Common insulator film materials are silicon dioxide (SiO2), aluminum trioxide (Al2O3), tantalum pentoxide (Ta2O5), silicon nitride (Si3N4), and aluminum nitride (AlN). Interposing a thin oxide film between a metal film and a semiconductor allows the formation of the technologically important metal-oxide-semiconductor (MOS) device. Thick coatings of SiO2, with its low coefficient of thermal expansion, can be rf sputter deposited. Insulating layers of SiO2, silicon nitride (Si2N3), and glass are deposited by PECVD for encapsulation and insulation layers in semiconductor processing.

Electrically active films - Doped silicon films are used in semiconductor devices, and these films often are deposited by a very sophisticated PVD evaporation technique called molecular beam epitaxy (MBE) or a CVD technique of vapor phase epitaxy (VPE). Amorphous silicon for solar cells is deposited by PECVD on webs and rigid substrates. Electochromic films, which change optical transmission on the application of a voltage, depend on the diffusion of a mobile species in the film under an electrical field. Films of a material such as selenium can become electrically charged when exposed to light. Such films are used to hold the toner in photocopying machines.

Electrically Conductive Films - Metal films are the most common electrical conductor films. Metal films may be used as "blanket" metallizations or can be formed into discrete conductor lines ("stripes") by masking the substrate during deposition or by subsequent photolithographic etching processes. Conductor lines are used in hybrid microcircuit technology and in the manufacture of semiconductor devices. Often, the electrical conductors are multilayer films (stacks) where each layer has a function. For example, the conductor film stack might have the composition: glass-Ti-Pd-Cu-Au. The titanium (Ti) is the "glue" layer, the palladium (Pd) provides corrosion resistance, the copper (Cu) is an electrical conductor, and the gold (Au) provides corrosion protection. Deposited metal conductors in "vias" are used in establishing electrical contacts between different layers in semiconductor device manufacturing. Blanket metallization is used to provide electromagnetic interference (EMI) and radio frequency interference (RFI) shielding on structures such as the plastic cases for cellular phones, electrodes for rigid and flexible capacitor electrodes, and surfaces for radar "chaff." Metal nitride, carbide, and silicide films generally are electrically conductive (Si3N4 and AlN are important exceptions). In some applications, films of these refractory materials are used to provide diffusion barriers between materials. For example, in semiconductor metallization, aluminum or gold electrode material will diffuse into the silicon during high-temperature processing. An electrically conductive titanium nitride film deposited on the silicon surface before the metal electrode is deposited will prevent the diffusion. Generating stable, electrically conductive, nonrectifying, metal semiconductor contacts of metals or metal-silicide compounds is an important aspect of semiconductor device fabrication. Metal nitrides such as tantalum nitride (TaN) are used as thin film resistor materials. Nontransparent electrically conductive oxides such as chromium trioxide (Cr2O3), lead oxide (PbO), and ruthenium oxygen (RuO) are used as electrodes in high-temperature oxidizing atmospheres. Superconductors are materials that have close to zero electrical resistivity below some critical temperature (Tc). Low- Tc (less than [<] 10 Kelvin [K]) superconductors are often metals. A typical high- Tc (greater than [>] 50 K) superconductor material is a mixture of oxides (yttrium-bismuth-copper [Y-Bi-Cu] oxides, YBCO). High- Tc superconductor thin films are often deposited by laser ablation in vacuum.

Electrochemical cell - An electrochemical system consisting of an anode and a cathode in metallic contact and immersed in an electrolyte. (The anode and cathode may be different metals or dissimilar areas on the same metal surface.

Electroless Nickel - The autocatalytic deposition of nickel/phosphorous and nickel/boron have many useful corrosion and tribo/corrosion applications. Unlike the electrolytic processes, they produce a deposit with completely uniform coverage. In the case of Ni P, deposits around 25 to 50 microns thick with a hardness of about 500Hv is obtained, but thermal ageing at temperatures around 400°C can develop hardness values in excess of 1000Hv.

Electrolyte - A conducting medium in which the flow of current is accompanied by movement of matter. A substance that is capable of forming a conducting liquid medium when dissolved or melted.

Electrolysis - Production of chemical changes of the electrolyte by the passage of current through an electrochemical cell.

Electromotive Force Series (EMF Series) - A list of elements arranged according to their standard electrode potentials, with "noble" metals such as gold being positive and "active" metals such as zinc being negative.

Electron-beam heat treating – A selective surface hardening process that rapidly heats a surface by direct bombardment with an accelerated stream of electrons.

Electroplating - The application of a layer of metal onto a substrate in a conducting solution of metal slats.

Elongation – In tensile testing, the increase in the gage length, measured after fracture of the specimen within the gage length, usually expressed as a percentage of the original gage length.

Embrittlement – The severe loss of ductility or toughness or both of a material, usually a metal or alloy. Many forms of embrittlement can lead to brittle fracture. Many forms can occur during thermal treatment or elevated-temperature service (thermally induced embrittlement). Some of these forms of embrittlement, which affect steels, include blue brittleness, 475°C (885°F) embrittlement, quench-age embrittlement, sigma-phase embrittlement, strain-age embrittlement, temper embrittlement, tempered martensite embrittlement, and thermal embrittlement. In addition, steels and other metals and alloys can be embrittled by environmental conditions (environmentally assisted embrittlement). The forms of environmental embrittlement include acid embrittlement, caustic embrittlement, corrosion embrittlement, creep-rupture embrittlement, hydrogen embrittlement, liquid metal embrittlement, neutron embrittlement, solder embrittlement, solid metal embrittlement, and stress-corrosion cracking.

Enantiotropy – The relation of crystal forms of the same substance in which one form is stable above a certain temperature and the other form stable below that temperature. Ferrite and austenite are enantiotropic in ferrous alloys, for example.

End-quench hardenability test – A laboratory procedure for determining the hardenability of a steel or other ferrous alloy; widely referred to as the Jominy test. Hardenability is determined by heating a standard specimen in a fixture so that a stream of cold water impinges on one end, and, after cooling to room temperature is completed, measuring the hardness near the surface of the specimen at regularly spaced intervals along its length. The data is normally plotted as hardness versus distance from the quenched end.

Energy Dispersive X-ray (SEM-EDX) - An electron beam microprobe for X-ray-fluorescence analysis. Commonly associated with electronic microscopy, it permits measuring the elementary composition of materials.

Entrainment - The sucking in of fluid from outside the shroud or nozzle of a plasma spray gun. To conserve momentum, the total momentum of the entrained flow must balance the total momentum of the expelled fluid.

Epitaxy - A film is called epitaxial when its crystallographic order is being significantly influenced by that of the substrate as a result of some degree of matching between the two along the interface.

Equilibrium diagram – A graphical representation of the temperature, pressure, and composition limits of phase fields in an alloy system as they exist under conditions of complete equilibrium. In metal systems, pressure is usually considered constant.

Erosion - Removal of material from a surface caused by the flow of particles within a liquid or gas.

Erosion-corrosion - Associated action involving corrosion and erosion in the presence of a corrosive substance.

Etch - A roughened surface produced by chemical, electrochemical or mechanical means. To dissolve unevenly a part of the surface of a material to highlight microstructure in metallography.

Eutectic – (1) An isothermal reversible reaction in which a liquid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. (2) An alloy having the composition indicated by the eutectic point on an equilibrium diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectic reaction.

Eutectic carbide – Carbide formed during freezing as one of the mutually insoluble phases participating in the eutectic reaction of ferrous alloys.

Eutectic melting – Melting of localized microscopic areas whose composition corresponds to that of the eutectic in the system.

Eutectoid – (1) An isothermal reversible reaction in which a solid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. (2) An alloy having the composition indicated by the eutectoid point on an equilibrium diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectoid reaction.

Exfoliation - Corrosion that proceeds laterally from the sites of initiation along planes parallel to the surface, generally at grain boundaries or coating interfaces, forming corrosion products that force metal or coating away from the body of the material, giving rise to a layered appearance.

Exothermic reaction of material - Certain materials undergo chemical reactions when heated in an arc or plasma and produce extra heating. This can be useful in improving adhesion of the coating to the substrate. There is also a potential explosive or fire hazard when handling powders which are exothermic.

Explosive cladding –Coatings applied by explosive gas mixture. Also called cladding.

Extensometer – An instrument for measuring changes in length caused by application or removal of a force. Commonly used in tension testing of metal specimens.

Extra hard – A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength and hardness about one-third of the way from full hard to extra spring hard.

Extra spring – A temper of nonferrous alloys and some ferrous alloys corresponding approximately to a cold-worked state above full hard beyond which further cold work will not measurably increase the strength and hardness.

---

F

Fatigue - A cumulative effect causing a metal to fail after repeated applications of stress none of which exceeds the ultimate tensile strength. The fatigue strength (or fatigue limits) is the stress that will cause failure after specified number cycles.

Fatigue Crack or Failure - A fracture starting from a nucleus where there is an abnormal concentration of cyclic stress. The fracture surface is smooth and frequently shows concentric (sea shell) markings with a nucleus as a center.

Fatigue Limit (Endurance Limit) - Maximum stress that a material will endure without failure for an infinite number of load cycles.

Fatigue Strength - Maximum stress that a material will endure without failure for a specified number of load cycles.

Fatigue wear - Wear of a solid surface caused by fracture arising from material fatigue.

Feeding - The process of supplying molten metal to compensate for volume shrinkage while the casting is solidifying.

Ferrite – A solid solution of one or more elements in body-centered cubic iron. Unless otherwise designated (for instance, as chromium ferrite), the solute is generally assumed to be carbon. On some equilibrium diagrams, there are two ferrite regions separated by an austenite area. The lower area is alpha ferrite; the upper, delta ferrite. If there is no designation, alpha ferrite is assumed.

Ferritizing anneal – A treatment given as-cast gray or ductile (nodular) iron to produce an essentially ferritic matrix. For the term to be meaningful, the final microstructure desired or the time-temperature cycle used must be specified.

Filler - A solid inert material added to a synthetic resin or rubber, either to change its physical properties or simply to dilute it for economy.

Final annealing – An imprecise term used to denote the last anneal given to a nonferrous alloy prior to shipment.

Fines - The portion of a powder composed of particles which are smaller than the specified size

Finish annealing – A subcritical annealing treatment applied to cold-worked low- or medium-carbon steel. Finish annealing, which is a compromise treatment, lowers residual stresses, thereby minimizing the risk of distortion in machining while retaining most of the benefits to machinability contributed by cold working. Compare with final annealing.

Finishing temperature – The temperature at which hot working is completed.

Finite difference - A numerical method of solving the Navier-Stokes equations, where the domain is divided up into small areas/volumes, with nodes (or grid points) placed at each corner. The fluid is then considered to exist only at these nodes. The difference between the nodes describes the property gradients in the fluid.

Finite element - A numerical method of solving the Navier-Stokes equations, where the domain is divided up into small areas/volumes. A shape function is then placed over the volume, it should be representative of the shape of the variation over the volume.

Finite volume - A numerical method of solving the Navier-Stokes equations, where the domain is divided up into small areas/volumes, and the flow properties are considered to be constant across the volume.

Fixturing – The placing of parts to be heat treated in a constraining or semi constraining apparatus to avoid heat-related distortions. See racking.

Flame annealing – Annealing in which the heat is applied directly by a flame.

Flame hardening – A process for hardening the surfaces of hardenable ferrous alloys in which an intense flame is used to heat the surface layers above the upper transformation temperature, whereupon the work piece is immediately quenched.

Flame spraying - A thermal spraying process in which the particles are heated and accelerated in a flame produced from the combustion of oxygen and fuel.

Flame straightening – Correcting distortion in metal structures by localized heating with a gas flame.

Fluidized-bed heating – Heating carried out in a medium of solid particles suspended in a flow of gas.

Fog quenching – A quench utilizing blasts of compressed air against relatively small parts such as a gear.

Forced-air quench – A quench utilizing blasts of compressed air against relatively small parts such as a gear.

Free carbon – The part of the total carbon in steel or cast iron that is present in elemental form as graphite or temper carbon. Contrast with combined carbon.

Free ferrite – Ferrite that is formed directly from the decomposition of hypoeutectoid austenite during cooling, without the simultaneous formation of cementite. Also called proeutectoid ferrite.

Freestanding structures - Freestanding structures can be made by depositing a coating on a surface (mandrel), then separating the coating from the mandrel surface or dissolving the mandrel. The technique is useful for fabricating very thin structures, complex surfaces, or foils or sheets of materials that are hard to deform by rolling. Examples are beryllium windows used for X-ray transmission, boron thin-wall cones for high-frequency audio speakers, and Ti-V-Al metal alloy foils. A relatively new application is the production of microelectromechanical systems (MEMS) devices where very small structures are fabricated using deposition and etching processes.

Freezing range – That temperature range between liquidus and solidus temperatures in which molten and solid constituents exist.

Fretting - Surface damage caused by very small relative movement between two surfaces usually under heavy load.

Fretting corrosion - A form of fretting wear in which corrosion plays a significant role.

Fretting wear - Wear arising as a result of fretting.

Friction - The reaction force resulting from surface interaction and adhesion during sliding. The friction Coefficient is defined as the friction force divided by the load.

Frictional Wear - The displacement and/or detachment of metallic particles from a surface as a consequence of being in contact with another moving component.

Full annealing – An imprecise term that denotes an annealing cycle to produce minimum strength and hardness. For the term to be meaningful, the composition and starting condition of the material and the time-temperature cycle used must be stated.

Full hard – A temper of nonferrous alloys and some ferrous alloys corresponding approximately to a cold-worked state beyond which the material can no longer be formed by bending. In specifications, a full hard temper is commonly defined in terms of minimum hardness or minimum tensile strength (or, alternatively, a range of hardness or strength) corresponding to a specific percentage of cold reduction following a full anneal. For aluminum, a full hard temper is equivalent to a reduction of 75% from dead soft; for austenitic stainless steels, a reduction of about 50 to 55%.

Fused and crushed powder - Powder formed from a fused solid mass which is then crushed to the appropriate size for spraying.

Fused coatings - A process in which the coating material is deposited by thermal spraying and then fused by post heat treatment. This can be done by flame, induction heating, furnace or by laser.

---

G

Galling - Damage to the surfaces of materials sliding in contact with each other, usually caused by the localized welding together of high spots. Common for materials like stainless steel, aluminum alloys and titanium.

Galvanic corrosion - Accelerated corrosion of a metal because of an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte.

Galvanic Series - A list of metals and alloys arranged according to their relative corrosion potentials in a given environment.

Galvanized - The process of coating steel with zinc for corrosion resistance.

Galvanizing - A hot dip process for deposition of zinc for galvanic corrosion protection of steel.

Gamma iron – The face-centered cubic form of pure iron, stable from 910 to 1400°C (1670 to 2550°F).

Gas carburizing - See Carburizing.

Gas cyaniding – A misnomer for carbonitriding.

Gas flow rate - The flow rate of gas (e.g. liters per minute) through the spraying torch.

Gas nitriding – Also called nitriding.

Gas nitrocarburizing – Also called nitrocarburizing.

Gold plating - The electrolytic deposition of gold for decorative or electrical applications.

Grain-boundary liquidation – An advanced stage of overheating in which material in the region of austenitic grain boundaries melts. Also termed burning.

Grain coarsening – A heat treatment that produces excessively large austenitic grains.

Grain growth – An increase in the average size of the grains in polycrystalline metal, usually as a result of heating at elevated temperature.

Grain refiner – A material added to a molten metal to induce a finer-than-normal grain size in the final structure.

Grain size – For metals, a measure of the areas or volumes of grains in a polycrystalline material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, the grain size refers to that of the matrix unless otherwise specified. Grain sizes are reported in terms of number of grains per unit area or volume, average diameter, or as a grain-size number derived from area measurement.

Granular powder - Particles having approximately equidimensional nonspherical shapes.

Graphite - A black lamella solid with low friction, anti wear properties. The low friction is not sustained in vacuum. In air it can be used up to 400 °C.

Graphitic carbon – Free carbon in steel or cast iron. See graphitization.

Graphitization – Formation of graphite in iron or steel. Where graphite is formed during solidification, the phenomenon is called primary graphitization; where formed later by heat treatment, secondary graphitization.

Graphitizing – Annealing a ferrous alloy in such a way that some or all of the carbon is precipitated as graphite.

Grinding - The removal of material by the use of fixed abrasives like grinding wheels or emery paper.

Grit blasting - A pressurized stream of hard metal or oxide grit material used to clean and/or roughen surfaces prior to coating.

Grossmann chart – A chart describing the ability of a quenching medium to extract heat from a hot steel work piece in comparison to still water.

Guinier-Preston (G-P) zone – A small precipitation domain in a supersaturated metallic solid solution. A G-P zone has no well-defined crystalline structure of its own and contains an abnormally high concentration of solute atoms. The formation of G-P zones constitutes the first stage of precipitation and is usually accompanied by a change in properties of the solid solution in which they occur.

 

Hafnium Nitride (HN) - Gold colored ceramic, typically applied as a thin coating. Very hard (3500Hv). Used on cutting tools and forming tools and other surfaces needing wear resistance.

Half hard – A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength about midway between that of dead soft and full hard tempers.

Hardenability – The relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surface where the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure.

Hardening – Increasing the hardness by suitable treatment, usually involving heating and cooling. When applicable, the following more specific terms should be used: age hardening, flame hardening, induction hardening, laser hardening, precipitation hardening, and quench hardening.

Hard chrome plating - The electrolytic deposition of chromium to form a very hard (1000Hv), tough coating with good wear resistance. The structure is micro-cracked.

Hardfacing - The application of a cladding or coating of material designed to resist wear.

Hardness – Resistance of metal to plastic deformation, usually by indentation. However, the term may also refer to stiffness or temper, or to resistance to scratching, abrasion, or cutting. Indentation hardness may be measured by various hardness tests, such as Brinell, Rockwell, and Vickers.

Hardness profile – Hardness as a function of distance from a fixed reference point (usually from the surface).

Hard temper – Same as full hard temper.

HCD - See Hollow Cathode Discharge

Heat Resistant Coating - Any coating which during normal use must withstand temperatures of at least 204°C (400°F).

Heat tinting – Coloration of a metal surface through oxidation by heating to reveal details of the microstructure.

Heat-treatable alloy – An alloy that can be hardened by heat treatment.

Heat-treating film – A thin coating or film, usually an oxide, formed on the surface of metals during heat treatment.

Heat treatment – A combination of heating and cooling operations and applied to a metal or alloy to produce desired properties and microstructures. Heating for the sole purpose of hot working is excluded from the meaning of this definition.

Helium (He) - Monatomic noble gas, Most inert element, atomic number 2. Used as a plasma gas in plasma spraying.

High-Alloy Steel - Ferrous alloy with more than 12 weight percent of noncarbon additions.

High Pressure Mold - A strong high-density mold, made by air, hydraulic, or other squeeze process.

High Strength Low Alloy Steel (HSLA) - Steel with relatively high strength and impact properties. The carbon level is low and the alloying additions are significantly less than 5 weight percent.

High Velocity Oxy-fuel Spraying (HVOF) - A Thermal spray process. The spray powder particles are injected into a jet formed by the combustion of oxy-fuel, heated and accelerated to the work piece.

HIPPING - The high temperature/high pressure consolidation of a powder metallurgy component or thermally sprayed coating. Density is greatly increased and metallurgical changes provide enhanced corrosion and wear properties.

Holding – The portion of the thermal cycle during which the temperature of the object is maintained constant.

Holding temperature – The constant temperature at which the object is maintained.

Holding time – Time for which the temperature of the object is maintained constant.

Hollow Cathode Discharge - A technique to deposit high quality TiN, CrN, TiCN, and TiCrN thin films on cutting tools, machine parts, molds, etc
Homogeneous carburizing – Use of a carburizing process to convert a low-carbon ferrous alloy to one of uniform and higher carbon content throughout the section.

Homogenizing – Holding at high temperature to eliminate or decrease chemical segregation by diffusion.

Horizontal batch furnace – A versatile batch-type furnace that can give light or deep case depths, and because the parts are not exposed to air, horizontal batch furnaces can give surfaces almost entirely free of oxides.

Hot dip coating - A metallic coating obtained by dipping the substrate metal into a molten metal.

Hot quenching – An imprecise term used to cover a variety of quenching procedures in which a quenching medium is maintained at a prescribed temperature above 70°C (160°F).

Hot-wire analyzer – An electrical atmosphere analysis device that is based on the fact that the electrical resistivity of steel is a linear function of carbon content over a range from 0.05% C to saturation. The device measures the carbon potential of furnace atmospheres (typically). This term is not to be confused with hot-wire test, which measures heat extraction rates.

HVOF - See High Velocity Oxy-fuel spraying.

Hydrogen (H2) - Diatomic gas, atomic number 1, The lightest element, very reactive and powerful reducing agent. Used as a secondary plasma gas in the plasma spraying process and as a fuel gas in combustion thermal spray processes (CWS, CPS and HVOF)

Hydrogen embrittlement - Hydrogen induced cracking or severe loss of ductility caused by the presence of hydrogen in the metal. Hydrogen absorption may occur during electroplating, pickling etc. ( The use of hydrogen as a secondary gas in plasma spraying does not appear to effect substrates and the majority of coatings, one exception being titanium coatings.)

Hydrophilic - Tending to absorb water.

Hydrophobic - Tending to repel water or lacking affinity for water

Hydroxyapatite - Hydroxyapatite is a biocompatible ceramic. It may be deposited by plasma spray onto orthopedic implants in order to increase the bone-implant contact. It may also be sprayed over a porous titanium coating where it is used to promote bone ingrowth.

Hypereutectic alloy – In an alloy system exhibiting a eutectic, any alloy whose composition has an excess of alloying element compared with eutectic composition, and whose equilibrium microstructure contains some eutectic structure.

Hypereutectoid alloy – In an alloy system exhibiting a eutectoid, any alloy whose composition has an excess of alloying element compared with the eutectoid composition, and whose equilibrium microstructure contains some eutectoid structure.

Hypereutectoid Steel - A steel containing more than the eutectoid percentage of carbon (0.83 wt. %).

Hypoeutectic alloy – In an alloy system exhibiting a eutectic, any alloy whose composition has an excess of based metal compared with the eutectic composition, and whose equilibrium microstructure contains some eutectic structure.

Hypereutectoid alloy – In an alloy system exhibiting a eutectoid, any alloy whose composition has an excess of base metal compared with the eutectoid composition, and whose equilibrium microstructure contains some eutectoid structure.

---

I

Ideal critical diameter (DI) – Under an ideal quench condition, the bar diameter that has 50% martensite at the center of the bar when the surface is cooled at an infinitely rapid rate (that is, when H = , where H is the quench severity factor).

Immersed-electrodes furnace – A furnace used for liquid carburizing of parts by heating molten salt baths with the use of electrodes immersed in the liquid. See submerged-electrode furnace.

Impact test - A test to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, as in the Charpy or Izod tests.

Impurity - An element unintentionally allowed in a metal or alloy. Some impurities have little effect on properties; others will grossly damage the alloy.

Inclusions - Particles of impurities (usually oxides, sulphides, silicates and such) which separate from the liquid steel and are mechanically held during solidification. In some grades of steel, inclusions are made intentionally high to aid machinability.

Indentation method for hardness and modulus measurements – An indenter tip with a known geometry is driven into a specific site of the material to be tested by applying an increasing normal load. When reaching a preset maximum value, the normal load is reduced until partial or complete relaxation. This procedure is performed repetitively; at each stage of the experiment the position of the indenter relative to the sample surface is precisely monitored. For each loading/unloading cycle, the applied load value is plotted with respect to the corresponding position of the indenter. The resulting load/displacement curves provide data specific to the mechanical nature of the material under examination. Established models are used to calculate quantitative hardness and modulus values from such data.

Indium-tin oxide (ITO) - Transparent semiconducting material used as an electrode on flat-panel displays and other electro-optical devices.

Impingement - A process resulting in a continuing succession of impacts between (liquid or solid) particles and a solid surface.

Impingement corrosion - a form of erosion-corrosion generally associated with the impingement of a high velocity, flowing liquid containing air bubbles against a solid surface.

Induction hardening – A surface-hardening process in which only the surface layer of a suitable ferrous work piece is heated above 900°C by electromagnetic induction to above the upper critical temperature and immediately quenched.

Induction heating - The heating of a electrically conductive material by an induction coil producing alternating magnetic fields which induce alternating electric currents to flow in the material and cause heating by resistance. Used in many heating process (induction fusing, induction plasma, induction hardening etc..)

Induction tempering – Tempering of steel using low-frequency electrical induction heating.

Infrared analyzer – An atmosphere-monitoring device that measures a gas (usually carbon monoxide, carbon dioxide, and methane) presence based on specific wavelength absorption of infrared energy.

Ingot - A casting of a simple shape which can be used for hot working or remelting.

Injection Molding - The injection of molten metal or other material under pressure into molds.

Insert - A part usually formed from metal, which is placed in a mold and may become an integral part of the casting.

Intense quenching – Quenching in which the quenching medium is cooling the part at a rate at least two and a half times faster than still water. See Grossmann chart.

Interconnected porosity - A network of pores in and extending to the surface of a coating.

Intercritical annealing – Any annealing treatment that involves heating to, and holding at, a temperature between the upper and lower critical temperatures to obtain partial austentization, followed by either slow cooling or holding at a temperature below the lower critical temperature.

Intergranular – Between crystals or grains. Also called intercrystalline. Contrast with transgranular.

Intergranular corrosion - Preferential corrosion at or adjacent to the grain boundaries of a metal or alloy.

Intergranular cracking – Cracking or fracturing that occurs between the grains or crystals in a polycrystalline aggregate. Also called intercrystalline cracking. Contrast with transgranular cracking.

Intergranular fracture – Brittle fracture of a metal in which the fracture is between the grains, or crystals, that form the metal. Also called intercrystalline fracture. Contrast with transgranular fracture.

Intermediate annealing – Annealing wrought metals at one or more stages during manufacture and before final treatment.

Internal Friction - Ability of a metal to transform vibratory energy into heat; generally refers to low stress levels of vibration; damping has a broader connotation since it may refer to stresses approaching or exceeding yield strength.

Internal oxidation - The formation of isolated particles of corrosion products beneath the surface of the metal or coating. (This occurs as a result of preferential oxidation of certain alloy constituents by inward diffusion of oxygen, nitrogen, sulfur, etc.

Internal Shrinkage - A void or network of voids within a casting caused by inadequate feeding of that section during solidification.

Internal Stresses - Generally stresses which occur during the cooling of a part.

Interrupted aging– Aging at two or more temperatures, by steps, and cooling to room temperature after each step. See aging, and compare with progressive aging and step aging.

Interrupted quenching – A quenching procedure in which the work piece is removed from the first quench at a temperature substantially higher than that of the quenchant and is then subjected to a second quenching system having a different cooling rate than the first.

Interval test – Method used to test heat extraction rates of various quenchants. This test measures the increase in temperature of a quenchant when a standard bar of metal is quenched for five seconds. Faster quenchants will exhibit greater temperature increases.

Ion carburizing – A method of surface hardening in which carbon ions are diffused into a work piece in a vacuum through the use of high-voltage electrical energy. Synonymous with plasma carburizing or glow-discharge carburizing.

Ion nitriding – A method of surface hardening in which nitrogen ions are diffused into a work piece in a vacuum through the sue of high-voltage electrical energy. Synonymous with plasma nitriding or glow-discharge nitriding.

Ion plating - A process in which positive ions produced in a glow discharge are attracted to the substrate which is connected as the cathode. The ions are typically made by evaporation.

Ion scattering spectroscopy - Surface sensitive technique where the depth of analysis can be limited to the outermost atomic layer. In ISS a low-energy monoenergetic beam of ions is focused onto a solid surface and the energy of the scattered ions is measured at a fixed angle. A primary beam of an inert gas (He+, Ne+, Ar+) is usually employed, and since the collision with the atoms on the surface can be considered as elastic, the energy loss identifies the element on the surface.

Ion-Implantation - A process in which a beam of positive ions is projected towards and into the surface. It is carried out in partial vacuum and the ions diffuse into the surface layer of the substrate. Typically this is carried out with nitrogen giving a nitrided effect.

Irregular powder - Particles lacking symmetry.

Isothermal annealing – Austenitizing a ferrous alloy and then cooling to and holding at a temperature at which austenite transforms to a relatively soft ferrite carbide aggregate.

Isothermal transformation – A change in phase that takes place at a constant temperature. The time required for transformation to be completed, and in some instances the time delay before transformation begins, depends on the amount of supercooling below (or superheating above) the equilibrium temperature for the same transformation.

Isothermal transformation (IT) diagram – Set of curves drawn using logarithmic time and linear temperature as coordinates, which define for each level of temperature the beginning and end of the transformation of the initial phase under isothermal conditions.

---

J

Jobbing Foundry - A foundry engaged in the manufacture of numerous types of castings.

Jominy test – See end-quench hardenability test.

---

K

Kerosene - Liquid fuel used in some HVOF thermal spray processes.

Killed steel - Steel treated with a strong deoxidizer to reduce oxygen to a level where no reaction occurs between carbon and oxygen during solidification.

Kish – Free graphite that forms in molten hypereutectic cast iron as it cools. In castings, the Kish may segregate toward the cope surface, where it lodges at or immediately beneath the casting surface

 

Ladle - Metal receptacle frequently lined with refractories used for transporting and pouring molten metal. Types include hand bull, crane, bottom-pour, holding, teapot, shank, lip-pour.

Laminar flow - The flow regime which exists when Reynolds Number is below 2000. The path lines of the particles are smooth and regular, and there is little interchange of fluid mass between adjacent layers.

Lapping - Rubbing two surfaces together, with or without abrasives, for the purpose obtaining extreme dimensional accuracy or superior surface finish.

Lap - A surface imperfection which appears as a seam. It is caused by the folding over of hot metal, fins, or sharp corners and then rolling or forging them into the surface but not welding them. Laps on tubes can form from seams on piercing mill billets.

Laser Ablation - A deposition technique which uses a pulsed UV laser beam for vaporizing solid source materials. Much of the material ablates as macroparticles rather than vaporizing as atoms or molecules. A key advantage is that it can achieve congruent evaporation of complex materials, such as mixed oxides.

Laser alloying - The application of a powder to a surface followed by fusing and alloying into the surface via the heat from an impinging laser.

Laser glazing - The melting and quenching of a surface to form a fine grained structure or 'glaze'.

Laser hardening – A surface-hardening process which uses a laser to quickly heat a surface above 900°C. Heat conduction into the interior of the part will quickly cool the surface, leaving a shallow martensitic layer.

Latent heat – Thermal energy absorbed or released when a substance undergoes a phase change.

Lead (Pb) - improves machinability. It does not dissolve in steel but stays as globules. Environmental concerns are resulting in a decreased usage of lead in the steel industry.

Ledeburite – The eutectic of the iron-carbon system, the constituents being austenite and cementite. The austenite decomposes into ferrite and cementite on cooling below the Ar1.

Leidenfrost phenomenon – Slow cooling rates associated with a hot vapor blanket that surrounds a part being quenched in a liquid medium such as water. The gaseous vapor envelope acts as an insulator, thus slowing the cooling rate.

Liquation temperature – The lowest temperature at which partial melting can occur in an alloy that exhibits the greatest possible degree of saturation.

Liquid carburizing – Surface hardening of steel by immersion into a molten bath consisting of cyanides and other salts.

Liquid impingement erosion - Progressive loss of material from a solid surface due to continue exposure to impacts by liquid drops or jets.

Liquid nitriding – A method of surface hardening in which molten nitrogen-bearing, fused salt baths containing both cyanides and cyanates are exposed to parts at subcritical temperatures.

Liquid nitrocarburizing – A nitrocarburizing process (where both carbon and nitrogen are absorbed into the surface) utilizing molten liquid salt baths below the lower critical temperature.

Liquid spray quench – Same as spray quenching.

Localized corrosion - Corrosion at discrete sites, for example, pitting, crevice corrosion, and stress corrosion cracking.

Localized precipitation – Precipitation from a supersaturated solid solution similar to continuous precipitation, except that the precipitate particles form at preferred locations, such as along slip planes, grain boundaries, or incoherent twin boundaries.

Low Activation Interior Coating - Any Coating used on the interior of ships to minimize the activation of pigments on painted surfaces within a radiation environment.

LPPS - See Vacuum or Low Pressure Plasma Spraying.

Lubricant - Any substance interposed between two surfaces for the purpose of reducing the friction or wear between them.

---

M

Macrohardness - The hardness of a coating as measured on a macroscopic scale, which shows the coatings bulk properties.
Magnetic Storage Media - Magnetic materials are classified as "hard" or "soft" depending on how hard it is to magnetize, demagnetize, or "switch" the magnetic field. Soft magnetic materials, such as the Permalloys (iron [Fe]:40 to 80% Ni) and Y2Fe5O12 (garnet) are used in memory storage devices where the data are changed often. Hard magnetic materials such as Fe3O4, Co:Ni:tungsten [W], Co:rhenium [Re], gadolinium [Gd]:Co, and Gd:terbium [Tb]:Fe are used in more permanent recording media such as audio tapes. Various techniques are used to define the magnetic domains that act as the storage sites.

Magnetic test – Method used to test heat extraction rates of various quenchants. The test works by utilizing the change in magnetic properties of metals at their Curie point – the temperature above which metals lose their magnetism.

Magnetron sputtering - In this PVD process, the sputtering action is enhanced by intense magnetic fields. Also called sputtering.

Malleable cast iron – A cast iron made by prolonged annealing of white cast iron in which decarburization or graphitization, or both, take place to eliminate some or all of the cementite. The graphite is in the form of temper carbon. If decarburization is the predominant reaction, the product will exhibit a light fracture surface, hence, “whiteheart malleable”; otherwise, the fracture surface will be dark, hence, “blackheart malleable.” Ferritic malleable has predominantly ferritic matrix; pearlitic malleable may contain pearlitic, spherodite, or tempered martensite depending on heat treatment and desired hardness.

Malleablizing – Annealing white cast iron in such a way that some or all of the combined carbon is transformed to graphite or, in some instances, part of the carbon is removed completely.

Manganese (Mn) - is important because it deoxidizes the melt and facilitates hot working of the steel by reducing the susceptibility to hot shortness. It combines with sulfur to form MnS stringers which increases machinability. Manganese contributes to the effectiveness of normalizing for strengthening, to the formation of fine pearlite, and lowers the Ms temperature, therefore increasing the probability of retained austenite.

Maraging – A precipitation-hardening treatment applied to a special group of iron-base alloys to precipitate one or more intermetallic compounds in a matrix of essentially carbon-free martensite.

Marine Coating - Any coating, except unsaturated polyester resin (fiberglass) coatings, containing volatile organic materials and applied by any means to ships, boats, and their appurtenances, and to buoys and oil drilling rigs intended for the marine environment.

Marquenching – See martempering.

Martempering – (1) A hardening procedure in which an austenitized ferrous work piece is quenched into an appropriate medium whose temperature is maintained substantially at the Ms of the work piece, held in the medium until its temperature is uniform throughout – but not long enough to permit bainite to form – and then cooled in air. The treatment is frequently followed by tempering. (2) When the process is applied to carburized material, the controlling Ms temperature is that of the case. This variation of the process is frequently called marquenching.

Martensite – A generic term for microstructures formed by diffusionless phase transformation in which the parent and product phases have a specific crystallographic relationship. Martensite is characterized by an acicular pattern in the microstructure in both ferrous and nonferrous alloys. In alloys where the solute atoms occupy interstitial positions in the marensite lattice (such as carbon in iron), the structure is hard and highly strained; but where the solute atoms occupy substitutional positions (such as nickel in iron), the martensite is soft and ductile. The amount of high-temperature phase that transforms to martensite on cooling depends to a large extent on the lowest temperature attained, there being a rather distinct beginning temperature (Ms) and a temperature at which the transformation is essentially complete (Mf).

Martensite range – The temperature interval between Ms and Mf.

Martensitic Stainless Steels - A corrosion-resistant ferrous alloy with a predominant martensitic phase.

Martensitic transformation – A reaction that takes place in some metals on cooling, with the formation of an acicular structure called martensite.

Mass Effect - The effect that the mass of a component has on the properties of the material from which the part is made. In castings such effects may arise due to the effect of mass on the solidification and on the rate of temperature change heat treatment.

Matrix - The continuous phase of a material or coating in which separate particles of another constituent are embedded. (Like tungsten carbide particles in a cobalt matrix)

McQuaid-Ehn test – A test to reveal grain size after heating into the austenitic temperature range. Eight standard McQuaid-Ehn grain sizes rate the structure, No. 8 being finest, No. 1 coarsest.

MCrAlY - MCrAlY's (where M = Ni, Co or Fe) are a group of high temperature, corrosion resistant alloys used to combat sulfidation and oxidation.

Mechanical bonding - Usually represented by mechanical interlocking of the deposited particles with the rough heights on the substrate surface produced during grit blasting.

Mechanical properties – The properties of material that reveals its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications: for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit. Compare with physical properties.

Mechanical testing – Determination of mechanical properties.

Mesh - The area made up of elements and nodes (or grid points) in a numerical simulation.

Metal – An opaque lustrous elemental chemical substance that is a good conductor of heat and electricity and, when polished, a good reflector of light. Most elemental metals are malleable and ductile and are, in general, denser than the other elemental substances.

Metallic Coating - Coating which contains more than 5 grams of metal particles per liter of coating, as applied.

Metallurgical bonding - Produced by chemical bonding between areas of the coating and substrate in intimate contact or even by diffusional interaction between the coating and substrate. Metallurgical bonding can be enhanced by post diffusion heat treatments.

Metallographic Structure - The nature, distribution, and amounts of the metallographic constituents in a metal.

Metallurgy – The science and technology of metals and alloys. Process metallurgy is concerned with the extraction of metals from their ores and with refining of metals; physical metallurgy, with the physical and mechanical properties of metals as affected by composition, processing, and environmental conditions; and mechanical metallurgy, with the response of metals to applied forces.

Mf Temperature – For any alloy system, the temperature at which martensite formation on cooling is essentially finished. See transformation temperature for the definition applicable to ferrous alloys.

Micrograph - A micrograph is produced when a section of the coating is taken, polished to show the particulate layers and then photographed through a microscope.

Microhardness – The hardness of a material as determined by forcing an indenter such as a Vickers or Knoop indenter into the surface of a material under very light load; usually, the indentations are so small that they must be measured with a microscope. Capable of determining hardness of different microconstituents within a structure, or a measuring steep hardness gradients such as those encountered in case hardening.

Microinch - One millionth of an inch, 0.000001".

Micrometer (µm) - One millionth of a meter, 0.001mm.

Microscopic stresses – Residual stresses that vary from tension to compression in a distance (presumably approximating the grain size) that is small compared with the gage length in ordinary strain measurements. They are not detectable by dissection methods, but can sometimes be measured from the line shift or line broadening in an x-ray diffraction pattern.

Microsegregation – Segregation within a grain, crystal, or small particle.

Microstructure - The structure of a metal as revealed at high magnification, usually at 100x and higher.

Microtrack - A device for measuring powder particle size distributions.

Mil - One thousandth of an inch, 0.001"

Mill scale – The heavy oxide layer formed during hot fabrication or heat treatment of metals.

Minus sieve - The portion of a powder sample which passes through a standard sieve of specified number e.g. -140 mesh +325 mesh. See Plus sieve.

Modulus Of Elasticity (E) - In tension it is the ratio of stress to the corresponding strain within the limit of elasticity (Yield Point) of a material. For carbon and low alloy steels any composition and treatment, the value is approximately 200 GPa or 30,000,000 psi.

Modulus of Resilience (ur) - The amount of strain energy per unit volume required to stress a material from zero to the yield stress limit. The modulus of resilience is proportional to the area under the elastic portion of the stress-strain diagram. Units are Pa or psi.

Modulus of Rigidity - In a torsion test the ratio of the unit shear stress to the displacement caused by it per unit length in the elastic range.

Modulus of Rupture - Used in both bending and torsion testing. In bending, the modulus of rupture is the bending moment at fracture divided by the section modulus. In torsion, modulus of rupture is the torque at fracture divided by the polar section modulus.

Modulus of Toughness (ut) - Amount of work per unit volume of a material required to carry that material to failure under static loading. Equal to the area under the entire stress-strain curve. Units are Pa or psi.

Mold Coating (Mold Facing, Dressing) – (1) Coating to prevent surface defects on permanent mold castings and die castings. (2) Coating on sand molds to prevent metal penetration and improve metal finish.

Molybdenum (Mo) - increases hardenability of steels and helps maintain a specified hardenability. It increases high temperature tensile and creep strengths. Molybdenum hardened steels require higher tempering temperatures for softening purposes. A metal used widely in alloying of other metals. It is used as hardening element for steel, and for diecasting dies. Melting point 2620°C (4748°F), atomic number 42.

Molybdenum Disulphide (MoS2) - A black, lamella structured solid with low sliding friction. Often applied as a powder filler to lubricants or dispersed in a polymer coating.

Monotropism – The ability of a solid to exist in two or more forms (crystal structures), but in which one form is the stable modification at all temperatures and pressures. Ferrite and martensite are a monotropic pair below Ac1 in steels, for example. May also be spelled monotrophism.

Ms temperature – For any alloy system, the temperature at which martensite starts to form on cooling. See transformation temperature for the definition applicable to ferrous alloys.

Multiport nozzle (Plasma) - Constricted nozzle with two or more internal bores, in order to achieve a better control of the shape and stability of plasma arc.

 

Natural aging – Spontaneous aging of a supersaturated solid solution at room temperature. See aging, and compare with artificial aging.

Navier-Stokes Equations - Probably the most pivotal equations in all of theoretical fluid dynamics, these equations relate all the flow field variables together into nonlinear partial differential equations. The NS equations are basically a reformulation of Newtons 2nd Law of a Motion, F=ma.

NCA - See notched coating adhesion.

Neutral flame – A gas flame in which there is no excess of either fuel or oxygen in the inner flame. Oxygen from ambient air is used to complete the combustion of CO2 and H2 produced in the inner flame.

Neutralization number – An ASTM number given to quenching oils that reflects the oil’s tendency toward oxidation and sludging. See saponification number.

Nickel (Ni) - is used in low alloy steels to reduce the sensitivity of the steel to variations in heat treatment and distortion and cracking on quenching. It also improves low temperature toughness and hardenability melting point 1455°C (2651°F). Nickel is also a base metal for many casting alloys resistant to corrosion and high temperature oxidation.

Nickel plating - The electrolytic deposition of nickel to form a corrosion barrier or to reclaim a worn part. Can also include hard ceramic particles to from a wear resistant composite coating.

Ni-Hard - Hard white cast iron containing 4% Ni and 2% Cr.
Niobium (Nb) (Columbium - Cb) - lowers transition temperature and raises the strength of low carbon steel. Niobium increases strength at elevated temperatures, results in finer grain size and forms stable carbides, lowering the hardenability of the steel.

Nitrogen (N) - increases the strength, hardness and machinability of steel, but it decreases the ductility and toughness. In aluminum killed steels, nitrogen combines with the aluminum to provide grain size control, thereby improving both toughness and strength. Nitrogen can reduce the effect of boron on the hardenability of steels.

Nitriding – Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous appropriate composition. Quenching is not required to produce a hard case. See aerated bath nitriding, bright nitriding, and liquid nitriding.

Nitrocarburizing – Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is done mainly to provide an antiscuffing surface layer and to improve fatigue resistance. Compare with carbonitriding.

Nitrogen (N2) - Diatomic gas. Used as a primary and secondary gas in plasma spraying. Inert to most materials, with some exceptions like titanium.

Noble metal - A metal that does not readily tend to furnish ions, and therefore does not dissolve readily, or easily enter into such reactions as oxidation, etc. The opposite of base metal.

Node - Used in a numerical simulation to attach the adjacent elements.

Nodular powder - Irregular particles having Knotted, rounded, or similar shapes.

Nonferrous - A negative term, refers to alloy in which the predominate metal or solvent is not iron.

Non transferred arc (Plasma) - The plasma arc which transfers heat energy to plasmagenic gas (Argon, Helium, Hydrogen, Nitrogen) in order to promote the plasma state according to the Saha's law. This arc strikes between the tungsten electrode (cathode) and the constricting nozzle (anode). The term Pilot Arc is also used in Plasma Transferred Arc process (P.T.A. welding).

Normal Steel - Steel in which the pearlite is completely laminated.

Normalizing – Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range.

Notched Coating Adhesion (NCA) - A recent characterization technique (test) used to analyze adhesive bond durability.

Nuclear Reaction Analysis (NRA) - An ion beam technique which allows light mass elements profiling into materials. Analysis depth up to one micrometer.

Nucleation – The initiation of a phase transformation at discrete sites, the new phase growing on nuclei. See nucleus.

Nucleus – The first structurally stable particle capable of initiating recrystallization of a phase or the growth of a new phase, and possessing an interface with the parent matrix. The term is also applied to a foreign particle that initiates such action.

---

O

Oil hardening – Quench-hardening treatment involving cooling in oil.

Oil quenching – Hardening of carbon steel in an oil bath. Oils are categorized as conventional, fast, martempering, or hot quenching.

OMCVD - See Organic Metal Chemical Vapor Deposition.

Optical Films - Optical films, usually multilayer films ("stacks"), are films that affect the optical transmission or reflection of a surface. They are generally alternating layers of materials having high (germanium [Ge], Si, TiO2, zirconium dioxide [ZrO2], SiO, cerium dioxide [CeO2]) and low (magnesium fluoride [MgF2], SiO2) indices of refraction. A major application is the antireflection (AR) coatings on lenses. Optical film stacks can be used as optical filters. Neutral density or gray filters reduce the light intensity equally for all wavelengths; broadband filters affect the transmission of radiation over a wide wavelength range, while narrow or monochromatic filters affect transmission over a very narrow wavelength region. An example of a broadband filter is an "edge filter" that "cuts off" the ultraviolet (UV) emitted by a mercury vapor lamp. Examples of narrow-band filters are the color filters used in photography and in projectors. Some film stacks are a special type of optical film that has a color that is related to the angle-of-observation (OVIDs). These films allow holographic-like imaging. These OVID films are used as security devices to prevent counterfeiting. These films are an outgrowth of the interference-colored films used for decorative films and, when pulverized, as pigments.

Optical pyrometer – An instrument for measuring the temperature of heated material by comparing the intensity of light emitted with a known intensity of an incandescent lamp filament.

Order-disorder transformation – A phase change among two solid solutions having the same crystal structure, but in which the atoms of one phase (disordered) are randomly distributed; in the other, the different kinds of atoms occur in a regular sequence upon the crystal lattice, which is in an ordered arrangement. Compare with dissociation.

Order hardening – A low-temperature annealing treatment that permits short-range ordering of solute atoms within a matrix, which greatly impedes dislocation motion.

Orange Peel - A finish resembling the dimpled appearance of an orange peel.

Organic Metal Chemical Vapor Deposition (OMCVD) - This process uses metal organic reactants having a low cracking temperature. It allows deposition of metallic carbides such as CrC with a moderated process temperature (~400°C).

Orsat analyzer – An atmosphere analysis device in which gases are absorbed selectively (volumetric basis) by passing them through a series of preselected solvents.

Overaging – Aging under conditions of time and temperature greater than those required to obtain maximum change in a certain property, so that the property is altered in the direction of the initial value. See aging.

Overheating – Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working, or by a combination of working and heat treating, the overheating is known as burning.

Oxidation – (1) A reaction in which there is an increase in valence resulting from a loss of electrons. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.

Oxidized surface (on steel) – Surface having a thin, tightly adhering, oxidized skin (from straw to blue in color), extending in from the edge of a coil or sheet. Sometimes called annealing border.

Oxidizing - The production of a stable oxide layer on a steel component by heating in a controlled atmosphere. Provides corrosion protection and reduced friction.

Oxidizing agent – A compound that causes oxidation, thereby itself becoming reduced.

Oxidizing flame – A gas flame produced with excess oxygen in the inner flame.

Oxygen (O2 ) - Gas used to support combustion of fuel gases in combustion thermal spray processes. Achieves much higher flame temperatures than using air.

Oxygen probe – An atmosphere-monitoring device that electronically measures the difference between the partial pressure of oxygen in a furnace or furnace supply atmosphere and the external air.

---

P

Pack carburizing – A method of surface hardening of steel in which the parts are packed in a steel box with carburizing compound and heated to elevated temperatures.

Pack nitriding – A method of surface hardening of steel in which parts are packed in a steel box with the nitriding compound and heated to elevated temperatures.

PACVD - See Plasma Assisted Chemical Vapor Deposition

Paint - A coating including resin, a solvent, additives, pigments and, in some products, a diluent. Paints are generally opaque, and commonly represent the portion of the industry known as "architectural coatings."

Painting - The application of organic based layers (acrylics, etc) for corrosion protection and decorative purposes.

Partial annealing – An imprecise term used to denote a treatment given cold-worked material to reduce the strength to a controlled level or to effect stress relief. To be meaningful, the type of material, the degree of cold work, and the time-temperature schedule must be stated.

Particle - The metal powder which is introduced into a plasma spray gun. One of two phases after the fluid that are modeled in a two-phase flow plasma spray gun simulation.

Particle chemistry - The elements contained within the particles of a spray powder.

Particle size - The controlling lineal dimension of an individual particle as determined by analysis with sieves or other suitable means.

Particle size distribution - The percentage by weight, or by number, of each fraction into which a powder sample has been classified with respect to sieve number or microns.

Particles Induced Gamma-ray Emission (PIGE) - An ion beam technique particularly well suited for the determination of light mass element concentrations into materials. Analysis depth up to a few micrometers.

Particles Induced X-ray Emission (PIXE) - An ion beam technique used in surface science for stoichiometry analysis and trace elements quantification. Ideal for coating impurities analysis.

Passivation - The process in metal corrosion by which metals become passive.

Passivating - The post treatment (usually by chromating) of nickel, cadmium or zinc coatings to reduce their corrosion rates.

Passivator - A type of inhibitor which appreciably changes the potential of a metal to a more noble (positive) value.

Passive - The state of a metal surface characterized by low corrosion rates in a potential region that is strongly oxidizing for the metal.

Patenting – In wiremaking, a heat treatment applied to medium carbon or high-carbon steel before the drawing of wire or between drafts. This process consists of heating to a temperature above the transformation range and then cooling to a temperature below Ae1 in air or in a bath of molten lead or salt.

Pearlite – A metastable lamellar aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range.

Peeling - The detachment or partial detachment of a coating.

Peening - A stream of sharp material particles which break superficial fiber, reducing internal stress fields.

Penetration, Metal - Condition where molten metal has penetrated into the sand, resulting in a mixture of metal and sand adhering to the casting.

Perfluro Alkyle Ether (PFA) - Relatively hard long chain polymer with inert, orientated structure. Applied by spraying and then melt flowing at temperatures above 250°C. Combines non-stick with wear resistance.

Perfuoroether (FEP) - A soft long chain polymer with an inert, orientated structure. Applied by spraying and then melt flowing at 400°C. Excellent non-stick properties.

Permanent Mold - A metal mold of two or more parts; not an ingot mold. It is used repeatedly for the production of many casting of the same form.

Permeability - A property measured as a rate of passage of a liquid or gas through a coating.

Phase diagram – A graphical representation of the temperature and composition limits of phase fields in an alloy system as they actually exist under the specific conditions of heating or cooling (synonymous with constitution diagram). A phase diagram may be an equilibrium diagram, an approximation to an equilibrium diagram, or a representation of metastable conditions or phases. Compare with equilibrium diagram.

Phosphating - A conversion process for steel surfaces to enhance corrosion protection. It is often zinc based.

Phosphorus (P) - is generally restricted to below 0.04 weight percent to minimize its detrimental effect on ductility and toughness. Certain steels may contain higher levels to enhance machinability, strength and/or atmospheric corrosion resistance.

Photothermal NDE - An NDE technique for spayed coatings. A repeated pulse of heat, from a laser source, flows through the coating and substrate. The thermal signature is detected and related to the input signal thereby indicating coating thickness.

Physical properties – Properties of a metal or alloy that are relatively insensitive to structure and can be measured without the application of force; for example, density, electrical conductivity, coefficient of thermal expansion, magnetic permeability, and lattice parameter. Does not include chemical reactivity. Compare with mechanical properties.

Physical Vapor Deposition - A term covering all the vapor deposition processes including Ion plating, It does not include CVD as this is chemical not physical.

Pickling - An operation by which surface oxide (scale) is removed by chemical action. Sulfuric acid is typically used for carbon and low-alloy steels. After the acid bath, the steel is rinsed in water.

Pin-on-disk tribometer – A measuring device used to determine wear characteristics of material samples. A flat or sphere shaped contact (“pin”) is loaded onto the test sample (“disk”) with a precisely known force. The pin is mounted on a stiff lever, designed as a frictionless force transducer. As the disk is rotated, resulting frictional forces acting between the pin and the disk are measured by very small deflections of the lever. Wear coefficients for both the pin and disk material are calculated from the volume of the material lost during a specific friction run. This simple method facilitates the determination and study of friction and wear behavior of almost every solid-state material combination, with varying time, contact pressure, velocity, temperature, humidity, lubricants, etc.

Pipe - A cavity formed by shrinkage of the metal during solidification, usually occurring in a riser having feeder metal for the casting.

Pirani gage – An instrument used to measure the pressure inside a vacuum chamber. The gage measures electrical resistance in a wire filament which will change in temperature depending on atmospheric pressure.

Pitot gage – An instrument that measures the stagnation pressure of a flowing fluid, consisting of an open tube pointing into the fluid and connected to a pressure indicating device.

Plasma - Plasma is a gas (usually Argon, Helium, Nitrogen, Hydrogen) that has been heated to a sufficiently high temperature to become partially ionized and therefore electrically conductive. The term was introduced by Irving LANGMUIR in 1930.

Plasma Assisted Chemical Vapor Deposition - This process enables to reduce the high process temperature of CVD (commonly 800-1000°C) to the 150-250°C range. It allows for a larger panel of basic materials.

Plasma carburizing – Same as ion carburizing.

Plasma jet - A jet of highly ionized gas usually produced from a plasma torch. An electric arc is struck between a cathode and anode and is then blown through a nozzle to form the jet.

Plasma nitriding – Same as ion nitriding.

Plasma Spraying - A thermal spraying process in which the heat source is a plasma jet.

Plasma transferred arc – Also called transferred arc.

Plasma-Based Ultra-fine Particle Synthesis - A liquid precursor is atomized and injected into the plasma flame; the plasma synthesized particles are collected either as a deposit on a substrate or as a powder on an electrostatic precipitator.

Plenum (Plasma) - Space or chamber confined by the inner wall of the constricting nozzle and the cathodic electrode. The shape and size of this annular chamber play the highest role in Plasma Arc torches (welding, spraying).

Plastic deformation – The permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit.

Plus sieve - The portion of a powder sample retained on a sieve of specified number. See minus sieve.

Pitting-tribology - A form of wear characterized by the presence of surface cavities the formation of which is attributed to processes such as fatigue, local adhesion, or cavitation.

Pitting--corrosion - corrosion of a metal surface, confined to a point or small area, that takes the form of cavities

Plasma Transferred Arc (PTA) - Similar to the plasma spray process in that powder is sprayed through a plasma, but instead of being heated via a neutral plasma (carrying no electric current) the arc is transferred to the substrate (made to be the anode). This is a hot process and produces coatings similar to fused or weld hardfacing coatings.

Plowing - The formation of grooves by plastic deformation of the softer of two surfaces in relative motion.

Polishing - The smoothing of a material surface by means of the action of abrasive particles attached usually to a fabric cloth. The final mechanical step in metallographic preparation.

Polyester - A condensation polymer formed by the interaction of polyhydric alcohols and polybasic acids. They are used in the manufacture of glass-fiber products. See Alkyd resin.

Polymer - A substance having large molecules consisting of repeated units. There are a number of natural polymers, such as polysaccharides synthetic polymer are extensively used in plastics.

Polymer films - There is increasing interest in depositing organic and inorganic polymer films in vacuum. These films can be formed by condensation of a monomer followed by E-beam or UV curing to polymerize the monomer or by plasma polymerization of the monomer. The monomer precursor can yield a carbon, silicon, or boron-based polymer material often containing hydrogen, chlorine, or fluorine. Fluorine-containing films are used to form hydrophobic surfaces

Polymorphism – The property of a chemical substance crystallizing into two or more forms having different structures, such as diamond and graphite.

Polytetrafluorethylene (PTFE) - A long chain polymer with orientated structure providing low friction. Applied as a coating (by spraying or dipping and curing) or as powder additions to other coatings (for instance electroless nickel).

Porosity - The presence of pores or voids in a coating whether connected or not. Porosity is not the same as pull-out.

Postheating – Heating weldments immediately after welding, for tempering, for stress relieving, or for providing a controlled rate of cooling to prevent formation of a hard or brittle surface.

Pot annealing – Same as box annealing.

Pouring - Transfer of molten metal from furnace to ladle, ladle to ladle, or ladle into molds.

Powder coating - Polymeric coatings applied for corrosion protection on low friction. Applied dry with electrostatic attraction to the part

Powder gas flow rate - The flow rate of the gas propelling the powder into the plasma jet in plasma spraying.

Powder injection angle - The angle from which the powder is injected into the plasma jet in plasma spraying.

Pre-alloyed powder - A powder composed of two or more elements which are alloyed in the powder manufacturing process and in which the particles are of the same nominal composition throughout.

Precipitation hardening – Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening and aging.

Precipitation heat treatment – Artificial aging in which a constituent precipitates from a supersaturated solid solution.

Preheating – Heating before some further thermal or mechanical treatment. For tool steel, heating to an intermediate temperature, immediately before final austenitizing. For some nonferrous alloys, heating to a high temperature for a long time, to homogenize the structure before working. In welding and related processes, heating to an intermediate temperature for a short time immediately before welding, brazing, soldering, cutting, or thermal spraying.

Press quenching – A quench in which hot dies are pressed and aligned with a part before the quenching process begins. Then the part is placed in contact with a quenching medium in a controlled manner. This process avoids part distortion.

Pretreatment Coating - A coating which contains no more than 12 percents solids by weight, and at least 1/2-percent acid by weight, is used to provide surface etching, and is applied directly to metal surfaces to provide corrosion resistance, adhesion, and ease of stripping.

Process annealing – An imprecise term denoting various treatments used to improve workability. For the term to be meaningful, the condition of the material and the time-temperature cycle used must be stated.

Profile Tolerances - A system of locating and tolerancing developed to control the orientation of rough parts in machine fixtures. From locating points on the casting a "perfect profile" is established for all surfaces and features. A tolerance envelope surrounding that profile defines the limitations of an acceptable part.

Progressive aging – Aging by increasing the temperature in steps or continuously during the aging cycle. See aging and compare with interrupted aging and step aging.

Propane (C3H8) - Aliphatic hydrocarbon gas used as a fuel gas in thermal spray processes.

Propylene (C3H6) - Hydrocarbon gas used as a fuel gas in thermal spray processes. Higher flame temperature than hydrogen and propane.

Properties - Fluid or particle properties as used in a CFD simulation. Fluid properties would be: density, viscosity, volume of expansion; Particle properties would be: density, specific heat of evaporation.

Pseudocarburizing – See blank carburizing.

Pseudonitriding – See blank nitriding.

PSP - See Plasma-Based Ultra-fine Particle Synthesis

PTA welding - See Plasma Transferred Arc Welding

Pull-out - Pull-out occurs when particles are plucked from the coating during machining or grinding. Also occurs during metallographic preparation. It is sometimes confused with porosity.

Pusher furnace – A type of continuous furnace in which parts to be heated are periodically charged into the furnace in containers, which are pushed along the hearth against a line of previously charged containers thus advancing the containers toward the discharge end of the furnace, where they are removed.

PVD - See Physical Vapor Deposition

Pyrometer – A device for measuring temperatures above the range of liquid thermometers

Quality Control - All aspects of the control of the spraying process including the surface preparation, spraying, control of thickness deposited and the oxide and porosity levels, surface finish and NDE checks as specified.

Quarter hard – A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength about midway between that of dead soft and half hard tempers.

Quench-age embrittlement – of low-carbon steels resulting from precipitation of solute carbons at existing dislocations and from precipitation hardening of the steel caused by differences in ferrite at different temperatures. Quench-age embrittlement usually is caused by rapid cooling of the steel from temperatures slightly below embrittlement Ac1 (the temperature at which austenite begins to form) and can be minimized by quenching from lower temperatures.

Quench aging – Aging induced by rapid cooling after solution heat treatment.

Quench annealing – Annealing an austenitic ferrous alloy by solution heat treatment followed by rapid quenching.

Quench Crack - A crack resulting from thermal stress induced during rapid cooling or quenching, or from stresses induced by delayed transformations some time after the article has been fully quenched.

Quench cracking – Fracture of a metal during quenching from elevated temperature. Most frequently observed in hardened carbon steel, alloy steel, or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners, or other stress raisers and result from high stresses due to the volume changes accompanying transformation to martensite.

Quench hardening – (1) Hardening suitable alpha-beta alloys (most often certain copper to titanium alloys) by solution treating and quenching to develop a martensitic-like structure. (2) In ferrous alloys, hardening by austenitizing and then cooling at a rate such that a substantial amount of austenite transforms to martensite.

Quenching – Rapid cooling. When applicable, the following more specific terms should be used: brine quenching, caustic quenching, cold die quenching, forced-air quenching, intense quenching, oil quenching, press quenching, spray quenching, direct quenching, fog quenching, hot quenching, interrupted quenching, and water quenching.

---

R

Racking – A term used to describe the placing of parts to be heat treated on a rack or tray. This is done to keep parts in a proper position to avoid heat-related distortions and to keep parts separated. See fixturing.

Recalescence – A phenomenon, associated with the transformation of gamma iron to alpha iron on cooling (supercooling) of iron or steel, revealed by the brightening (reglowing) of the metal surface owing to the sudden increase in temperature caused by the fast liberation of the latent heat of transformation. Contrast with decalescence.

Recarburize – (1) To increase the carbon content of molten cast iron or steel by adding carbonaceous material, high-carbon pig iron, or a high-carbon alloy. (2) To carburize a metal part to return surface carbon lost in processing; also known as carbon restoration.

Recovery – Reduction or removal of work-hardening effects, without motion of large-angle grain boundaries.

Recrystallization – (1) The formation of a new, strain-free grain structure from that existing in cold-worked metal, usually accomplished by heating. (2) The change from one crystal structure to another, as occurs on heating or cooling through a critical temperature.

Recrystallization annealing – Annealing cold-worked metal to produce a new grain structure without phase change.

Recrystallization temperature – The approximate minimum temperature at which complete recrystallization of a cold-worked metal occurs within a specified time.

Recuperator – Equipment for transferring heat from gaseous products of combustion to incoming air or fuel. The incoming material passes through pipes surrounded by a chamber through which the outgoing gases pass.

Reducing Agent - A substance that causes reduction, thereby itself becoming oxidized.

Reducing flame – A gas flame produced with excess fuel in the inner flame.

Reduction - A reaction in which electrons are added to the reactant. More specifically, the addition of hydrogen or the abstraction of oxygen.

Reduction of area – (1) Commonly, the difference, expressed as a percentage of original area, between the original cross-sectional area of a tensile test specimen and the minimum cross-sectional area measured after complete separation. (2) The difference, expressed as a percentage of original area, between original cross-sectional area and that after straining of the specimen.

Refractory – (1) A material of very high melting point with properties that make it suitable for such uses as furnace linings and kiln construction. (2) The quality of resisting heat.

Regenerator – Same as recuperator except the gaseous products of combustion heat brick checkerwork in a chamber connected to the exhaust side of the furnace while the incoming air and fuel are being heated by the brick checkerwork in a second chamber, connected to the entrance side. At intervals, the gas flow is reversed so that incoming air and fuel contact hot checkerwork while that in the second chamber is being reheated by exhaust gases.

Residual stress – An internal stress not depending on external forces resulting from such factors as cold working, phase changes, or temperature gradients.

Resin - A synthetic or naturally occurring polymer.

Retort – A vessel used for distillation of volatile materials, as in separation of some metals and in destructive distillation of coal.

Reverberatory furnace – A furnace with a shallow hearth, usually nonregenerative, having a roof that deflects the flame and radiates heat toward the hearth or the surface of the charge.

RFI Shielding - Thermal spray coatings of electrically conductive metals such as zinc, aluminum and copper are used on non-conducting composite casing materials to shield sensitive electronic devices from radio frequency electromagnetic interference.

Rhodium plating - The electrodeposition of rhodium for oxidation resistance combined with surface hardness.

Rimmed steel - A low carbon steel having enough iron oxide to give a continuous evolution of carbon monoxide during solidification giving a rim of material virtually free of voids.

Rockwell hardness test – An indentation hardness test based on the depth of penetration of a specified penetrator into the specimen under certain arbitrarily fixed conditions.

Rotary retort furnace – A continuous-type furnace in which the work advances by means of an internal spiral, which gives good control of the retention time within the heated chamber.

Runout - A casting defect caused by incomplete filling of the mold due to molten metal draining or leaking out of some part of the mold cavity during pouring; escape of molten metal from a furnace, mold or melting crucible.

Rutherford Backscattering Spectrometry (RBS) - A relevant ion beam technique for surface composition analysis (analyzed depth: up to 1 micrometer). It is widely used in thin film science.

S

Salt bath carburizing - See Carburizing.

Salt bath heat treatment – Heat treatment carried out in a bath of molten salt.

Salt bath nitriding - See Nitriding.

Salt bath nitrocarburizing - See Nitrocarburizing.

Salt spray test - Accelerated testing of corrosion properties of metallic coatings

Sand - In metalcasting, a loose, granular material high in SiO2, resulting from the disintegration of rock. The name sand refers to the size of grain and not to mineral composition. Diameter of the individual grains can vary from approximately 6 to 270 mesh. Most foundry sands are made up principally of the mineral quartz (silica). Reason for this is that sand is plentiful, refractory, and cheap; miscellaneous sands include zircon, olivine, chromite, CaCO3, black sand (lava grains), titanium minerals and others.

Sand Casting - Metal castings produced in a green sand, dried sand or core sand mold.

Sand Control - Procedure whereby various properties of foundry sand, such as fineness, permeability, green strength, moisture content, etc., are adjusted to obtain castings free from blows, scabs, veins, and similar defects.

Sand Porosity - Volume of the pore spaces or folds in sand. Not synonymous with permeability.

Saponification number – A number given to quenching oils that reflects the oils amount of compounding with fatty materials, which thereby helps evaluate the condition of these oils in service. See neutralization number.

Scab - An expansion discontinuity defect on the surface of a casting which appears as a rough, slightly raised surface blemish, crusted over by a thin porous layer of metal under which is a honeycomb or cavity that usually contains a layer of sand.

Scaling (Scale) - Surface oxidation, partially adherent layers of corrosion products, left on metals by heating or casting in air or in other oxidizing atmospheres.

Scanning probe microscopy (SPM) – An extremely accurate and versatile technique for measuring structures or surface forces. A very fine sensor tip mounted to the end of a small deflecting spring, known as a cantilever, is brought into contact with the sample surface to be investigated. The sensor tip is moved across the surface in numerous line scans. Due to the surface roughness (topography), the tip and the cantilever move up and down. This movement can be measured with high resolution and the resulting data allows imaging of the surface structure. Also called atomic force microscopy.

Scanning Tunneling Microscopy - Technique to directly observe individual atoms on surfaces. In STM a solid specimen in air, liquid or vacuum is scanned by a sharp tip located very close to the surface. A quantum -mechanical tunneling current flows between atoms on the surface and those on the tip. The magnitude of the current depends upon the separation between the surface and tip atoms, so that it is possible to obtain surface topography with atomic resolution.

Scarfing - Cutting off surface projections such as gates and risers from casting by means of gas torch.

Scoring - A severe form of wear characterized by the formation of extensive grooves and scratches in the direction of sliding.

Scrap Metal - Metal to be remelted; includes scrapped machinery fabricated items such as rail or structural steel and rejected castings.

Scratching - The mechanical removal or displacement, or both, of material from a surface by the action of abrasive particles or protuberances sliding across the surfaces.

Screen Analysis - Distribution of particle size sand expressed in terms of the percentage of weight retained on each of a series of standard screens decreasing in mesh size and the percentage passed by the screen of finest mesh.

Sealant, Sealer - A preparation of resin or wax type materials for sealing the porosity in coatings.

Sealing - A process which, by absorption of a sealer into thermal spray coatings, seals porosity and increases resistance to corrosion of the underlying substrate material.

Seam - A defect on the surface of a metal which appears as a crack. Experience indicates that most seams are created during the cooling or reheating of cast structures.

Secondary hardness - The higher hardness developed by certain alloy steels when they are cooled from a tempering operation. This should always be followed by a second tempering operation.

Selective heating – Intentionally heating only certain portions of a work piece.

Selective quenching – Quenching only certain portions of an object.

Self-bonding coatings - A name given to thermal spray coatings that are capable of bonding to clean smooth surfaces. Bond and "one-step" coatings are normally in this group. These are particularly important where grit blasting or surface roughening processes must be omitted.

Self-hardening steel – See preferred term, air-hardening steel.

Semi-killed steel - Incompletely deoxidized steel which contains enough dissolved oxygen to react with the carbon to form carbon monoxide to offset solidification shrinkage.

Sensitization – In austenitic stainless steels, the precipitation of chromium carbides, usually at grain boundaries, on exposure to temperatures of about 540 to 845°C (1000 to 1550°F), leaving the grain boundaries depleted of chromium and therefore susceptible to preferential attack by a corroding (oxidizing) medium.

Severity of quench – Ability of quenching medium to extract heat from a hot steel work piece; expressed in terms of H value.

Shaker-hearth furnace – A continuous-type furnace that uses a reciprocating shaker motion to move the parts along the hearth.

Shear - A type of deformation in which parallel planes in the metal crystals slide so as to retain their parallel relation.

Shear Modulus (G) - In a torsion test, the ratio of the unit shear stress to the displacement caused by it per unit length in the elastic range. Units are Pa or psi.

Shear Strain - Elastic displacement produced by pure shear loading.

Shear Strength - Maximum shear stress a material is capable of withstanding without failure.

Shell hardening – A surface-hardening process in which a suitable steel work piece, when heated through and quench hardened, develops a martensitic layer or shell that closely follows the contour of the piece and surrounds a core of essentially pearlitic transformation product. This result is accomplished by a proper balance among section size, steel hardenability, and severity of quench.

Shell Molding - A process for forming a mold from resin-bonded sand mixtures brought in contact with pre-heated (150-250°C / 300-500°F) metal patterns, resulting in a firm shell with a cavity corresponding to the outline of the pattern.

Shift - A casting defect caused by mismatch of cope and drag or of cores and mold.

Shim – A thin piece of material placed between two surfaces to obtain a proper fit, adjustment, or alignment. The piece can also be analyzed to measure furnace carbon potential (that is, because while in the furnace it will quickly carburize to a level equal to the furnace carbon potential).

Shot peening - The bombardment of a component surface with steel or ceramic shot. Produces a residual compressive stress in the surface and improves fatigue and stress corrosion performance.

Shrinkage - A decrease in dimensions of a coating during processing.

Shrinkage stress - The residual stress in a coating caused by shrinkage during processing.

Shroud - A gaseous and/or mechanical or physical barrier placed around the spraying process designed to reduce the ingress of air into the system and so reduce oxidation of the particles being sprayed.

Sieve Analysis - Distribution of particle size sand expressed in terms of the percentage of weight retained on each of a series of standard screens decreasing in mesh size and the percentage passed by the screen of finest mesh.

Sieve classification - That portion of a powder sample which passes through a standard sieve of specified number and is retained by some finer sieve of specified number.

Sigma phase – A hard, brittle, nonmagnetic intermediate phase with a tetragonal crystal structure, containing 30 atoms per unit cell occurring in many binary and ternary alloys of the transition elements. The composition of this phase in the various systems is not the same, and the phase usually exhibits a wide range in homogeneity. Alloying with a third transition element usually enlarges the field of homogeneity and extends it deep into the ternary section.

Sigma-phased embrittlement – Embrittlement of iron-chromium alloys (most notably austenitic stainless steels) caused by precipitation at grain boundaries of the hard, brittle intermetallic sigma phase during long periods of exposure to temperatures between approximately 565 and 980°C (1050 and 1800°F). Sigma-phase embrittlement results in severe loss in toughness and ductility and can make the embrittled material structure susceptible to intergranular corrosion. See also sensitization.

Signal-to-noise ratio – Ratio of the average response to the root-mean-square variation about the average response. Ratio of variances associated with the two parts of the performance measurement.

Silica Sand - Sand with a minimum silica content of 95% used for forming casting molds.

Silicon (Si) - is one of the principal deoxidizers with the amount used dependent on the deoxidization practice. It slightly increases the strength of ferrite without a serious loss of ductility. In larger quantities, it aids the resistance to scaling up to 500°F in air and decreases magnetic hysteresis loss.

Siliconizing – Diffusing silicon into solid metal, usually steel, at elevated temperature.

Silver plating - The electrodeposition of silver for electrical, decorative or anti-fretting properties.

Simulation - A procedure which describes, numerically, a given flow regime. The solution of the numerical method should replicate the real life flow characteristics.

Single Port Nozzle (Plasma) - Constricted nozzle with only one internal bore, concentric with the longitudinal axis of the tungsten electrode. The shape and design accuracy of this single orifice is decisive for arc stability in plasma welding.

Sintering – The bonding of adjacent surfaces in a mass of particles by molecular or atomic attraction on heating at high temperatures below the melting temperature of any constituent in the material. Sintering strengthens a powder mass and normally produces densification and, in powdered metals, recrystallization.

Size analysis - Analysis of the size of the particles being deposited by spraying processes.

Size distribution - The distribution of sizes within a size analysis. The distribution may be normal or skewed in some way due to the powder manufacturing process.

Skewed Tolerances - Tolerances which are non-symmetrically distributed about the design parameter.

Skim Core (Skimmer) - A flat core or tile placed in a mold to skim a flowing stream of metal. Commonly used in pouring basins, it holds back slag and dirt while clean metal passes underneath to the downsprue.

Skim Gate - A gating arrangement which changes the direction of flow of molten metal and prevents the passage of slag and other undesirable materials into the mold cavity.

Skimming - Removing or hold back dirt or slag from the surface of the molten metal before or during pouring.

Skin - A thin surface layer different chemically or structurally from the main mass of a metal object.

Skin-Drying - Drying the surface of the mold by direct application of heat.

Slack quenching – The incomplete hardening of steel due to quenching from the austenitizing temperature at a rate slower than the critical cooling rate for the particular steel, resulting in the formation of one or more transformation products in addition to martensite.

Slag Inclusion - Nonmetallic solids entrapped in solid metal.

Slag Trap - An enlargement, dam, or extrusion in the gating or runners system in a mold for the purpose of preventing molten slag particles from entering the mold cavity.

Slicking (Sleeking) - Smoothing the surface of molds.

Slot furnace – A common batch furnace where stock is charged and removed through a slot or opening.

Slurry - A term loosely applied to any clay-like dispersion. It may be use to wash ladles or other refractory linings to impart a smooth surface; as a bonding addition to molding sand; as a thin loam over specially made molds or as a mixture to fine joints or cracks of a core, etc.

Smelting - A metallurgical thermal process in which a metal is separated in fused form from nonmetallic materials or other undesired metals with which it is associated.

Snap temper – A precautionary interim stress-relieving treatment applied to high-hardenability steels immediately after quenching to prevent cracking because of delay in tempering them at the prescribed higher temperature.

Soaking – Prolonged holding at a selected temperature to effect homogenization of structure or composition.

Soft temper – Same as dead soft temper.

Solution heat treatment – Heating an alloy to a suitable temperature, holding at that temperature long enough to cause one or more constituents to enter into solid solution, and then cooling rapidly enough to hold these constituents in solution.

Sorbite – (obsolete) A fine mixture of ferrite and cementite produced either by regulating the rate of cooling of steel or by tempering steel after hardening. The first type is very fine pearlite difficult to resolve under the microscope; the second type is tempered martensite.

Spalling – A chipping or flaking of a surface due to any kind of improper heat treatment or material dissociation.

Specific Gravity - A numerical value representing the weight of a given substance as compared with the weight of an equal volume of water at 3.9°C (39°F), for which the specific gravity is taken as 1,000 kg/m3.

Specific Heat - Equivalent to thermal capacity, or the quantity of heat required to produce a unit change in the temperature of a unit mass.

Specific Volume - Volume of one gram of a substance at a specific temperature, usually 20°C (68°F).

Spinodal hardening – See aging.

Spheroidite – An aggregate of iron or alloy carbides of essentially spherical shape dispersed throughout a matrix of ferrite.

Spheroidizing – Heating and cooling to produce a spheroidal or globular form of carbide in steel. Spheroidizing methods frequently used are:

1.      Prolonged holding at a temperature just below Ae1

2.      Heating and cooling alternately between temperatures that are just above and just below Ae1

3.      Heating to a temperature above Ae1 or Ae3 and then cooling very slowly in the furnace or holding at a temperature just below Ae1

4.      Cooling at a suitable rate from the minimum temperature at which all carbide is dissolved, to prevent the reformation of a carbide network, and then reheating in accordance with method 1 or 2 above. (Applicable to hypereutectoid steel containing a carbide network.)

Spinodal structure – A fine homogeneous mixture of two phases that form by the growth of composition waves in a solid solution during suitable heat treatment. The phases of a spinodal structure differ in composition from each other and from the parent phase but have the same crystal structure as the parent phase.

Spray chamber - A chamber in which the spraying process is carried out. It may merely be an acoustic chamber for plasma spraying or a vacuum chamber for vacuum plasma spraying.

Spray dried powder - Powder formed by the spray drying process.

Spray-fused coatings - A process in which the coating material is deposited by flame spraying and then fused into the substrate by the addition of further heat. This can be applied by flame induction heating or by laser.

Spray quenching – A quenching process using spray nozzles to spray water or other liquids on a part. The quench rate is controlled by the velocity and volume of liquid per unit of time of impingement.

Spring temper – A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength and hardness about two-thirds of the way from full hard to extra spring temper.

Sputtering - This is a glow discharge process whereby bombardment of a cathode releases atoms from the surface which then deposit onto a nearby target surface to form a coating.

Stabilizing treatment – (1) Before finishing to final dimensions, repeatedly heating a ferrous or nonferrous part to or slightly above its normal operating temperature and then cooling to room temperature to ensure dimensional stability in service. (2) Transforming retained austenite in quenched hardenable steels, usually by cold treatment. (3) Heating a solution-treated stabilized grade of austenitic stainless steel to 870 to 900°C (1600 to 1650°F) to precipitate all carbon as TiC, NbC, or TaC so that sensitization is avoided on subsequent exposure to elevated temperature.

Stainless Steel - A wide range of steels containing chromium or chromium and nickel, exhibiting high resistance to corrosion.

Standard Deviation - A statistical quantity used to describe the variation of a measurable attribute about some average value.

Statistical process control – The application of statistical techniques for measuring and analyzing the variation in processes.

Statistical quality control – The application of statistical techniques for measuring and improving the quality of processes and products (includes statistical process control, diagnostic tools, sampling plans, and other statistical techniques).

Stead’s brittleness – A condition of brittleness that causes transcrystalline fracture in the coarse grain structure that results from prolonged annealing of thin sheets of low-carbon steel previously rolled at a temperature below about 705°C (1300°F). The fracture usually occurs at about 45° to the direction of rolling.

Steam tempering - The production of a stable oxide on steel parts by treatment in steam at about 300°C. Improves corrosion performance and reduces friction.

Steel - An alloy of iron and carbon that may contain other elements and in which the carbon content does not exceed about 1.7%; it must be malleable at some temperature while in the as-cast state.

Step aging – Aging at two or more temperature, by steps, without cooling to room temperature after each step. See aging, and compare with interrupted aging and progressive aging.

Sticker - A lump on the surface of a casting caused by a portion of the mold face sticking to the pattern. Also, a forming tool used in molding.

Strain - A measure of the extent to which a body is deformed when it is subjected to a stress.

Strain-age embrittlement – A loss in ductility accompanied by an increase in hardness and strength that occurs when low-carbon steel (especially rimmed or capped steel) is aged following plastic deformation. The degree of embrittlement is a function of aging time and temperature, occurring in a matter of minutes at about 200°C (400°F) but requiring a few hours to a year at room temperature.

Strain aging – Aging following plastic deformation.

Strand casting - Operation in which a cast shape is continuously drawn through the bottom of the mold as it solidifies. The length is not determined by mold dimensions.

Streamlines - A streamline is a line of fluid particles, the velocity of each particle is tangential to the line, the particle can not cross the streamline.

Stress - The force per unit area on body that tends to cause it to deform. It is a measure of the internal forces in a body between particles of the material of which it consists as they resist separation, compression, or sliding.

Stress-Corrosion Cracking - Spontaneous failure of metals by cracking under combined conditions of corrosion and stress, either residual or applied.

Stress equalizing – A low-temperature heat treatment used to balance stresses in cold-worked material without an appreciable decrease in the mechanical strength produced by cold working.

Stress relieve temper - A thermal treatment to restore elastic properties and to minimize distortion on subsequent machining or hardening operations. This treatment is usually applied to material that has been heat treated (quenched and tempered). Normal practice would be to heat to a temperature 100°F lower than the tempering temperatures used to establish mechanical properties and hardness. Ordinarily, no straightening is performed after the stress relieve temper.

Stress, Relieving - A heat treatment to reduce residual stresses followed by sufficiently slow cooling to minimize development of new residual stresses.

Stress, Residual - Those stresses setup up in a metal as a result of nonuniform plastic deformation or the unequal cooling of a casting.

Strike-Off - Operation of removing excess sand from top or core box or flask.

Stripping - Removing the pattern from the mold or core box from core.

Structurals - Steel product group that includes I-beams, H-beams, wide-flange beams and sheet piling. These products are used in the construction of multi-story buildings, industrial buildings, bridge trusses, vertical highway supports, and riverbank reinforcement.

Structure (Cast Structure) - The size and disposition of the constituents of a metal as cast.

Subcritical annealing – A process anneal performed on ferrous alloys at a temperature below Ac1.

Submerged-electrode furnace – A furnace used for liquid carburizing of parts by heating molten salt baths with the use of electrodes submerged in the ceramic lining. See immersed-electrode furnace.

Substrate - The parent or base material to which the coating is applied.

Sulfidation - The reaction of a metal or alloy with a sulfur containing species to produce a sulfur compound that forms on or beneath the surface of the metal or alloy.

Sulfur (S) - A nonmetallic element, melting point 444°C (831.2°F) occurring as an undesirable tramp (trace) element in most ferrous alloys. Detrimental to transverse strength and impact resistance. It affects longitudinal properties to a lesser degree. Existing primarily in the form of manganese sulfide stringers, sulfur is typically added to improve machinability.

Supercooling – Cooling below the temperature at which an equilibrium phase transformation takes place, without actually obtaining the transformation.

Superheating – Heating above the temperature at which an equilibrium phase transformation should occur without actually obtaining the transformation.

Surface Coating Operations - All operations involving the application of protective, decorative, adhesive or strengthening coating or impregnation to one or more surfaces, or into the interstices of any object or material, by means of spraying, spreading, flowing, brushing, roll coating, pouring, cementing or similar means; and any subsequent draining or drying operations, excluding open-tank operations.

Surface Hardening - Conferring a superficial hardness to a steel while maintaining a relatively soft core.

Surfacing - Depositing a filer metal on a metal surface by any method to obtain certain desired properties or dimensions.

Surface Texture - The roughness, waviness, lay or other characteristics of the surface of a part.

Surfacing - The application of a coating or cladding to a surface to impart a change in its surface behavior.

Stress-Corrosion Cracking - Spontaneous failure of metals by cracking under combined conditions of corrosion and stress, either residual or applied.

Surface energy - Surface energy exists because the molecules of a condensed phase are attracted to each other, which is what causes the condensation. The force required for the removal of molecular contact from above a surface, i.e. for the bond-breaking, is the surface energy.

Surface Finish (or Surface Texture) - A measure of the roughness of a surface by expressing the average deviation of the peaks and valleys from the mean line (denoted Ra).

Surface hardening – A generic term covering several processes applicable to a suitable ferrous alloy that produces, by quench hardening only, a surface layer that is harder or more wear resistant than the core. There is no significant alteration of the chemical composition of the surface layer. The processes commonly used are carbonitriding, carburizing, induction hardening, flame hardening, nitriding, and nitrocarburizing. Use of the applicable specific process name is preferred.

Surface parameter Ra - Arithmetical mean roughness: is the arithmetical average value of all departures of the surface profile from the mean line throughout the sampling length.

Surface parameter Rmax - It is the largest single peak-to-valley height within five adjoining sampling lengths 'le'.

Surface parameter Rt - Maximum roughness depth: is the distance between the highest and the lowest points of the surface profile within the evaluation length Lm.

Surface parameter Rz - Mean peak-to-valley height: is the average of the single peak-to-valley of five adjoining sampling lengths 'le'.

Surface preparation - Cleaning and roughening the surface to be sprayed, usually by grit or bead blasting. This is to increase the adhesion of the coating to the substrate.

Surface topography - The geometrical detail of a surface, relating particularly to microscopic variations in height.

Surface Treatment - General term denoting a treatment involving a modification of the surface: superficial heat treatment, diffusion treatment, conversion coating (consisting of a compound of the surface metal by chemical or electrochemical treatment).

Surfacing - The application of a coating or cladding to a surface to impart a change in its surface behavior.

Swell - A casting defect consisting of an increase in metal section due to the displacement of sand by metal pressure.

Synthetic Molding Sand - Any sand compounded from selected individual materials which, when mixed together, produce a mixture of the proper physical and mechanical properties from which to make foundry molds.

System Sand - Foundry sand used in making molds and which eventually becomes the bulk of the sand used in the mechanical system or mechanized unit.

Tellurium (Te) - is added to steel to modify sulfide type inclusion size, morphology and distribution. The resulting sulfide type inclusions are finer and remain ellipsoidal in shape following hot working, thereby improving transverse properties.

Temper – (1) In heat treatment, reheating hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness. The process also is sometimes applied to normalized steel. (2) In tool steels, temper is sometimes used, but inadvisably, to denote carbon content. (3) In nonferrous alloys and in some ferrous alloys (steels that cannot be hardened by heat treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties, or reduction in area during cold working.

Temper carbon – Same as annealing carbon.

Temper color – A thin, tightly adhering oxide skin that forms when steel is tempered at a low temperature, or for a short time, in air or a mildly oxidizing atmosphere. The color, which ranges from straw to blue depending on the thickness of the oxide skin, varies with both tempering time and temperature.

Tempered martensite embrittlement – Embrittlement of ultrahigh-strength steels caused by tempering in the temperature range of 205 to 400°C (400 to 750°F); also called 350°C or 500°F embrittlement. Tempered martensite embrittlement is thought to result from the combined effects of cementite precipitation on prior-austenite grain boundaries or interlath boundaries and the segregation of impurities at prior-austenite grain boundaries.

Temper embrittlement – Embrittlement of alloy steels caused by holding within or cooling slowly through a temperature range just below the transformation range. Embrittlement is the result of the segregation at grain boundaries of impurities such as arsenic, antimony, phosphorus, and tin; it is usually manifested as an upward shift in ductile-to-brittle transition by retempering above the critical temperature range, then cooling rapidly.

Temper Stressing - Quenching in water from the tempering temperature to improve fatigue strength.

Tempering - A treatment consisting of heating uniformly to some predetermined temperature under the critical range, holding at that temperature a designated period of time and cooling in air or liquid. This treatment is used to produce one or more of the following end results: A) to soften material for subsequent machining or cold working, B) to improve ductility and relieve stresses resulting from prior treatment or cold working, and C) to produce the desired mechanical properties or structure in the second step of a double treatment.

Temperature - Degree of warmth or coldness in relation to an arbitrary zero measured on one or more of accepted scales, as Centigrade, Fahrenheit, etc.

Tensile Strength - The maximum stress in uniaxial tension testing which a material will withstand prior to fracture. The ultimate tensile strength is calculated from the maximum load applied during the test divided by the original cross-sectional area. Compare with yield strength.

Tensile stress - Axial forces per unit area applied to a body that tend to extend it.

Thermal analysis – A method for determining transformations in a metal by noting the temperatures at which thermal arrests occur. These arrests are manifested by changes in slope of the plotted of mechanically traced heating and cooling curves. When such data are secured under nearly equilibrium conditions of heating and cooling, the method is commonly used for determining certain critical temperatures required for the construction of equilibrium diagrams.

Thermal barrier coating - A coating produced to present an insulating barrier to a heat source and to protect the substrate.

Thermal conductivity - The property of matter by which heat energy is transmitted through particles in contact. For engineering purposes, the amount of heat conducted through refractories is usually given in Btu per hour for one square foot of area, for a temperature difference of one degree Fahrenheit, and for a thickness of one inch, Btu/hr·ft·F/in.

Thermal Diffusion (TD) - A salt bath treatment at about 900°C for high carbon tool steels. Produces a very hard layer of vanadium carbide, typically .0002-.0003” thick. Also called Thermo-Reactive Diffusion (TRD).

Thermal electromotive force – The electromotive force generated in a circuit containing two dissimilar metals when one junction is at a temperature different from that of the other. See also thermocouple.

Thermal fatigue – Fracture resulting from the presence of temperature gradients that vary with time in such a manner as to produce cyclic stresses in a structure. Failure resulting from rapid cycles of alternate heating and cooling.

Thermal shock – Stress developed by rapid and uneven heating of a material.

Thermal spraying - A process in which coating material is heated and accelerated from a spray torch towards the work piece. The deposited material forms a coating on the surface.

Thermal stresses – Stresses in metal resulting from nonuniform temperature distribution. Usually occurs during the cooling of a part.

Thermochemically formed coatings - A painted, dipped or sprayed chromium oxide based coating consolidated by repeated deposition and curing cycles (about 500°C).

Thermochemical treatment – Heat treatment carried out in a medium suitably chosen to produce a change in the chemical composition of the object by exchange with the medium.

Thermocouple – A device for measuring temperatures, consisting of lengths of two dissimilar metals or alloys that are electrically joined at one end and connected to a voltage-measuring instrument at the other end. When one junction is hotter than the other, a thermal electromotive force is produced that is roughly proportional to the difference in temperature between the hot and cold junctions.

Thermography - An NDE technique in which the coating is flash heated and then viewed with an infra red camera. "Hot spots" indicate areas of poor bonding or greater coating thickness.

Thermomechanical working – A general term covering a variety of processes combining controlled thermal and deformation treatments to obtain specific properties. Same as thermal-mechanical treatment.

Three-quarters hard – A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength and hardness about midway between those of half hard and full hard tempers.

Time quenching – A term used to describe a quench in which the cooling rate of the part being quenched must be changed abruptly at some time during the cooling cycle.

Time-temperature-transformation (TTT) diagram – See isothermal transformation (IT) diagram.

Titanium (Ti) - is added to boron steels because it combines with oxygen and nitrogen, thus increasing the effectiveness of boron. Titanium, as titanium nitride, also provides grain size control at elevated temperatures in microalloy steels. In excess, titanium is detrimental to machinability and internal cleanness.

Titanium nitride (TiN) - Gold colored ceramic, typically applied as a thin coating by either PVD or CVD. Very hard (3500Hv). Used on cutting tools and forming tools and other surfaces requiring wear resistance

Tolerance - The permissible deviation of a dimension from the nominal or desired value. Minimum clearance between mating parts.

Tool Steel - Any high-carbon or alloy steel used to make a cutting tool for machining and forming metals and for metal-casting dies.

Total carbon – The sum of the free and combined carbon (including carbon in solution) in a ferrous alloy.

Total indicator reading – See preferred term total indicator variation.

Total indicator variation – The difference between the maximum and minimum indicator readings during a checking cycle.

Toughness – The ability of a metal to absorb energy and deform plastically before fracturing.

Trajectory - The path a particle takes when it’s injected into a stream of moving gas (or fluid). It is used in CFD to predict the path of the metal powder used in the plasma spray gun analysis.

Transcrystalline – See transgranular.

Transferred arc - In a plasma torch the plasma jet is emitted from the torch and the current flows from the internal cathode to the internal anode represented by the nozzle of the torch. When the jet is carried to another anode with it being electrically favorable to do so the current will then transfer to the second anode, usually the work piece and the arc is said to be transferred.

Transferred Arc (Plasma) - The plasma arc which transfers heat energy to the work piece (base material). This arc strikes between the tungsten electrode (cathode) and the base material (anode). The term Main Arc is also used in Plasma Transferred Arc process (P.T.A. welding).

Transformation hardening – Heat treatment comprising austenitization followed by cooling under conditions such that the austenite transforms more or less completely into martensite and possibly into bainite.

Transformation-induced plasticity – A phenomenon, occurring chiefly in certain highly alloyed steels that have been heat treated to produce metastable austenite or metastable austenite plus martensite, whereby, on subsequent deformation, part of the austenite undergoes strain-induced transformation to martensite. Steels capable of transforming in this manner, commonly referred to as TRIP steels, are highly plastic after heat treatment, but exhibit a very high rate of strain hardening and thus have high tensile and yield strengths after plastic deformation at temperatures between about 20 and 500°C (70 and 930°F). Cooling to -195°C (-320°F) may or may not be required to complete the transformation to martensite. Tempering usually is done following transformation.

Transformation ranges – Those ranges of temperature within which a phase forms during heating and transforms during cooling. The two ranges are distinct, sometimes overlapping but never coinciding. The limiting temperatures of the ranges depend on the composition of the alloy and on the rate of change of temperature, particularly during cooling. See transformation temperature.

Transformation temperature – The temperature at which a change in phase occurs. The term is sometimes used to denote the limiting temperature of a transformation range. The following symbols are used for iron and steels.

Accm – In hypereutectoid steel, the temperature at which the solution of cementite in austenite is completed during heating.

Ac1 – The temperature at which austenite begins to form during heating.

Ac3 – The temperature at which transformation of ferrite to austenite is completed during heating

Ac4 – The temperature at which austenite transforms to delta ferrite during heating.

A3cm, Ae1, Ae3, Ae4 – The temperature of phase changes at equilibrium.

Arcm – In hypereutectoid steel, the temperature at which precipitation of cementite starts during cooling.

Ar1 – The temperature at which transformation of austenite to ferrite or to ferrite plus cementite is completed during cooling.

Ar3 – The temperature at which austenite begins to transform to ferrite during cooling.

Ar4 – The temperature at which delta ferrite transforms to austenite during cooling.

Ar’ – The temperature at which transformation of austenite to pearlite starts during cooling.

Mf – The temperature at which transformation of austenite to martensite finishes during cooling.

Ms (or Ar”) – The temperature at which transformation of austenite to martensite starts during cooling.

Note: All these changes except the formation of martensite occur at lower temperatures during cooling than during heating, and depend on the rate of change of temperature.

Transgranular – Through or across crystals or grains. Also called intracrystalline or transcrystalline.

Transgranular cracking – Cracking or fracturing that occurs through or across a crystal or grain. Also called transcrystalline cracking. Contrast with intergranular cracking.

Transgranular fracture – Fracture through or across the crystals or grains of a metal. Also called transcrystalline fracture or intracrystalline fracture. Contrast with intergranular fracture.

Transition temperature – (1) An arbitrarily defined temperature that lies within the temperature range in which metal fracture characteristics (as usually determined by tests of notched specimens) change rapidly, such as from primarily fibrous (shear) to primarily crystalline (cleavage) fracture. Commonly used definitions are “transition temperature for 50% cleavage fracture,” “10 ft • lbf transition temperature,” and “transition temperature for half maximum energy.” (2) Sometimes used to denote an arbitrarily defined temperature within a range in which the ductility changes rapidly with temperature.

Transmission Electron Microscopy (TEM) - Applied to thin and thick film analysis, it permits observation of smaller features such as microcolumnar voids and patterns of dislocations in the bulk.

Transparent Electrical Conductors - Transparent conductive oxide (TCO) films, such as indium trioxide (In2O3), tin dioxide (SnO2), zinc oxide (ZnO) and an alloy of indium oxide and tin oxide (ITO), have numerous applications such as heaters on windows for defrosting, antistatic coatings on display screens, electrodes on flat panel displays and electrochromic devices, and electrodes on both flexible (resistive screen) and rigid (capacitive screen) touch screens. Electrical resistivity for the TCO films can vary from greater than 1,000 ohms per "square" to less than 10 ohms per square with good optical transmission.

Trap - This condition applies to a wall entity during a CFD analysis of a particulate two-phase flow. A particle touches the wall entity, its momentum and energy are assumed to be completely lost to the wall entity, while the mass is assumed lost to the fluid.

TRD (Thermo-Reactive Diffusion) - A salt bath treatment at about 900°C for high carbon tool steels. Produces a very hard layer of vanadium carbide, typically .0002-.0003” thick. Also called Thermal Diffusion (TD).

TRIP steel – A commercial steel product exhibiting transformation-induced plasticity.

Troostite – (obsolete) A previously unresolved rapidly etching fine aggregate of carbide and ferrite produced either by tempering martensite at low temperature or by quenching a steel at a rate slower than the critical cooling rate. Preferred terminology for the first product is tempered martensite; for the latter, fine pearlite.

Tungsten carbide - Metallic colored ceramic, often applied as a coating by thermal spraying. With a Co or Ni binder. Used for high load applications requiring extreme wear resistance.

Tungsten disulphide - Dry lubricant coating - applied at ambient temperature. Coating is 0.5 micron thick works at temperatures -273deg k to 650deg C. For use at high vacuum, cryogenic or high temperatures. Extends bearing life. Prevents galling, fretting & seizing. Can be applied to miniature ball races in assembled condition. Developed by NASA for use in deep space. Used in plastics industry as permanent release coating.

Turbulent flow - Technical terminology for the type of flow which occurs when the Reynolds Number exceeds 2000. In contrast to laminar flow, turbulent flow can be described as an irregular and random-looking motion.

Two-phase - Particular type of analysis where two of the three phases (gas, liquid and solid) are modeled together. The numerical equations are modified to produce an interaction between the two phases.

Ultrasonic - An NDE technique which relies on an ultrasonic beam passing through a coating and substrate and providing a signal from the back wall which is then detected. The height of this backwall echo depends on the discontinuity in impedance from the sprayed coating to the substrate. Bonding flaws can be easily seen by the weakening of the back wall echo.

Undercooling – Same as supercooling.

Upgrading - In castings, the removal and repair of discontinuities to raise the quality level of the casting beyond that which can be economically achieved by good foundry practice.

---

V

Vacuum annealing – Annealing carried out at subatmospheric pressure.

Vacuum carburizing – A high-temperature gas carburizing process using furnace pressures between 7 and 55kPa during the carburizing portion of the cycle.

Vacuum Casting - A casting in which metal is melted and poured under very low atmospheric pressure; a form of permanent mold casting where the mold is inserted into liquid metal, vacuum is applied, and metal drawn up into the cavity.

Vacuum furnace – A furnace using low atmospheric pressures instead of a protective gas atmosphere like most heat-treating furnaces. Vacuum furnaces are categorized as hot wall or cold wall, depending on the location of the heating and insulating components.

Vacuum or Low Pressure Plasma Spraying - Plasma spraying carried out in a chamber which has been evacuated to a low partial pressure of oxygen. It is then usually partially backfilled with argon to avoid the possibility of forming a glow discharge.

Vacuum Coating - Vacuum coatings processes use a vacuum (sub-atmospheric pressure) environment and an atomic or molecular condensable vapor source to deposit thin films and coatings. The vacuum environment is used not only to reduce gas particle density but also to limit gaseous contamination, establish partial pressures of inert and reactive gases, and control gas flow. The gaseous environment may be in the form of a partially ionized plasma. The vapor source may be from a solid or liquid surface (physical vapor deposition—PVD), or from a chemical vapor precursor (chemical vapor deposition—CVD). The term "vacuum deposition" is often used instead of PVD, particularly in the older literature. Vacuum is an environment where the gas pressure is less than the ambient. A plasma is a gaseous environment in which there are enough ions and electrons for there to be appreciable electrical conductivity. Vacuum coating is the deposition of a film or a coating in a vacuum (or low-pressure plasma) environment. Generally the term is applied to processes that deposit atoms (or molecules) one at a time such as physical vapor deposition (PVD) or low-pressure chemical vapor deposition (LP-CVD) processes or plasma-enhanced CVD (PECVD). In PVD processes, the material being deposited comes from the vaporization of a solid or liquid surface. In CVD processes, the material being deposited comes from a chemical vapor precursor species that is decomposed by reduction or thermal decomposition—mostly on a hot surface. In some cases the material being deposited reacts with the gaseous environment or a codeposited species to form a film of a compound material such as an oxide, a nitride, carbide, or a carbonitride. In CVD processing, the use of a plasma to fragment the chemical vapor precursor in the vapor phase allows the decomposition or reduction processes to proceed at lower temperatures than with thermal activation alone. PECVD can be performed at pressures as low as those used in PVD processing (low-pressure PECVD, LP-PECVD), where the precursor vapor is decomposed mainly in the plasma. In some cases a hybrid deposition process of PVD and LP-PECVD is used to deposit alloys, composites, or compounds. An example is metal carbonitrides where the carbon comes from a chemical vapor precursor such as acetylene; the nitrogen comes from a gas; and the metal from evaporation, sputtering, or arc vaporization of a solid or liquid surface.

Vacuum nitrocarburizing – A subatmospheric nitrocarburizing process using a basic atmosphere of 50% ammonia / 50% methane, containing controlled oxygen additions of up to 2%.

Vanadium (V) - inhibits grain growth during heat treating while improving strength and toughness of hardened and tempered steels. Additions up to .05% increase hardenability whereas larger amounts tend to reduce hardenability because of carbide formation. Vanadium is also utilized in ferrite/pearlite microalloy steels to increase hardness through carbonitride precipitation strengthening of the matrix.

Vector plot - A way of displaying results from a CFD analysis, where the velocity of each particle is visualized with an arrow. Since the arrow represents "velocity" it has a direction and magnitude (the length of the arrow indicates the relative magnitude)

Veins - A discontinuity on the surface of a casting appearing as a raised, narrow, linear ridge that forms upon cracking of the sand mold or core due to expansion of the sand during filling of the mold with molten metal.

Vickers hardness test – A microindentation hardness test employing a 136° diamond pyramid indenter (Vickers) and variable loads, enabling the use of one hardness scale for all ranges of hardness – from very soft lead to tungsten carbide. Also known as diamond pyramid hardness test.

---

W

Walking-beam furnace – A continuous-type furnace consisting of two sets of rails, one stationary and the other movable. Only the work being processed has to be heated because trays or fixtures are not needed.

Warpage - Deformation other than contraction that develops in a casting between solidification and room temperature; also, distortion occurring during annealing, stress relieving, and high-temperature service.

Wash - A casting defect resulting from erosion of sand by metal flowing over the mold or corded surfaces. They appear as rough spots and excess metal on the casting surface. Also called cuts.

Washburn Core - A thin core which constricts the riser at the point of attachment to the casting. The thin core heats quickly and promotes feeding of the casting. Riser removal cost is minimized.

Water quenching – A quench in which water is the quenching medium. The major disadvantage of water quenching is its poor efficiency at the beginning or hot stage of the quenching process.

Wear - Loss of material from a surface by means of relative motion between it and another body. Third bodies i.e. grit

Welding - A process used to join metals by the application of heat. Fusion welding, which includes gas, arc, and resistance welding, requires that the parent metals be melted.

Welding, Autogenous - Method of uniting two pieces of metal by melting their edges together without solder or any added welding metal, as by the thermite process that employs a medium of finely divided aluminum powder and oxide or iron by which a temperature of some 2982.2°C (5400°F) is obtained.

Welding Electrode - A metal or alloy in rod or wire forms used in electric arc welding to maintain the arc and at the same time supply molten metal or alloy at the point where the weld is to be
accomplished.

Welding Flash - Skin exposed too long to the ultraviolet rays of welding or melting arcs will burn as in a sunburn. Though temporary blindness can result, it is not permanent, as is popularly believed.

Welding Process - The joining of materials by the application of heat or friction.

Welding Stress - That stress resulting from localized heating and cooling of metal during welding.

White layer – Compound layer that forms as a result of the nitriding process.

Wire spraying - A thermal spray process whereby the supply for the coating material is fed into the gun in the form of a continuous wire.

Work hardness - Hardness developed in metal resulting from cold working.

---

X

X-Ray Diffraction (XRD) - A surface science technique for crystalline structure analysis of materials. Widely used both in the research and industrial area. analyzed depth up to 10 micrometers.

X-ray Photoelectron Spectroscopy (XPS) - An electron beam technique applied for near-surface elements identification and chemical state analysis. Widely used in thin film science. Analysis depth: a few Angstroms.

---

Y

Yield point - The first stress in a material, usually less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points.

Yield strength – The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2% is used for many metals. Compare with tensile strength.

---

Z

Zinc (Zn) - Thermal spray coatings of zinc or zinc alloys (e.g. Zn/Al, Zn/Sn) provides galvanic corrosion protection.

Zinc Plating - The electro deposition of zinc or zinc alloys (e.g. Zn/Ni, Zn/Sn) to provide galvanic corrosion protection