Glossary | E – G (The vocabulary of the coating and heat-treating industries—explained)

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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 / Young's Modulus

The parameter of a material that represents its stiffness. See also modulus of elasticity.


The description of how well a material can return to its original dimensions after an applied stress.

Electrical Insulators

Films that 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 metal-oxide-semiconductor (MOS) device, which is technologically important. 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. 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. 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) superconductors are often metals. A typical high-Tc (greater than 50 Kelvin) 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 (NiP) 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 NiP, deposits around 25 to 50 microns thick with a hardness of about 500Hv is obtained, but thermal aging at temperatures around 400°C can develop hardness values in excess of 1000Hv.


The instigation of chemical changes in the electrolyte via the passage of current through an electrochemical cell.


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

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 directly bombarding it with an accelerated stream of electrons.


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


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.


The severe loss of a material's ductility and/or toughness. Many forms of embrittlement can occur during thermal treatment or elevated-temperature service (thermally induced embrittlement), and many can lead to brittle fracture. 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.

Embrittlement, 475°C (885°F)

Embrittlement of stainless steels upon extended exposure to temperatures 400°C – 510°C (750°F – 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.


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. For example, ferrite and austenite are enantiotropic in ferrous alloys.

End-Quench Hardenability Test / Jominy 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.


The sucking in of fluid from outside the shroud/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.


A film is 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.


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


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


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


(object) An alloy having the composition indicated by the eutectic point on an equilibrium diagram.
(describes a structure) An alloy structure of intermixed solid constituents formed by a eutectic reaction.
(describes a reaction) 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.
Compare to eutectoid.

Eutectic Carbide

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

Eutectic Melting

The melting of localized microscopic areas whose composition corresponds to that of the eutectic in the system.


(object) An alloy having the composition indicated by the eutectoid point on an equilibrium diagram.
(describes a structure) An alloy structure of intermixed solid constituents formed by an eutectoid reaction.
(describes a structure) 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.
Compare to eutectic.


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. Gives 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 exothermic powders.

Explosive Cladding

Coatings applied by explosive gas mixture. Also called cladding.


An instrument for measuring changes in length caused by the 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 that is characterized by tensile strength and hardness about one-third of the way from full hard to extra spring hard.

Extra Spring Hard

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.



A cumulative effect causing a metal to fail after repeated applications of stress not exceeding the ultimate tensile strength.

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)

The maximum amount of stress that a material will endure, without failure, for an infinite number of load cycles. Compare with fatigue strength.

Fatigue Strength

The maximum amount of stress that a material will endure, without failure, for a specified number of load cycles. Compare with fatigue limit.

Fatigue Wear

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


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


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 for as-cast gray/ductile (nodular) iron that produces an essentially ferritic matrix. For the term to be meaningful, the final microstructure desired or the time-temperature cycle used must be specified.


A solid, inert material added to a synthetic resin/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.


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/medium-carbon steel. A compromise treatment that lowers residual stresses, thereby minimizing the risk of distortion in machining while retaining most of the machinability benefits garnered from cold working. Compare with final annealing.

Finishing Temperature

The temperature at which hot working is completed.

Finite Difference

One of the methods used to solve the Navier-Stokes Equations. 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. Compare to finite element and finite volume.

Finite Element

One of the methods used to solve the Navier-Stokes Equations. The domain is divided up into small areas/volumes. A shape function is then placed over the volume, and it should be representative of the shape of the variation over the volume. Compare to finite difference and finite volume.

Finite Volume

One of the methods used to solve the Navier-Stokes Equations. The domain is divided up into small areas/volumes and the flow properties are considered to be constant across the volume. Compare to finite difference and finite element.


The placing of parts to be heat-treated in a constraining / semi-constraining apparatus to avoid heat-related distortion. 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. The work piece is quenched immediately afterwards.

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

The rapid cooling of a part using fine vapor or mist.

Forced-Air Quench

A quench wherein compressed air is blasted 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

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, and foils and sheets made from 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.


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.


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 that corresponds 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.



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.


A hot dip process; the deposition of zinc onto steel for galvanic corrosion protection.

Gamma Iron

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

Gas Carburizing

See carburizing.

Gas Cyaniding

A misnomer for carbonitriding.

Gas Flow Rate

The rate, measured in liters per minute, at which gas flows through the spraying torch.

Gas Nitriding

See nitriding.

Gas Nitrocarburizing

See 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.


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

Graphitic Carbon

Free carbon in steel or cast iron. See graphitization.


The 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.


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


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.

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