Metallurgical Terms for the
Coating and Heat Treating Industries
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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 (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.
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