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, Zrthe "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 webswhich are then converted to decorative uses
such as balloons and labelsto 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 lubricantssuch as silver
and leadand the laminar-shearing compound materialssuch 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.
