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Glossary of Corrosion Related Terms
T
- Tafel Line, Tafel Slope, Tafel
Diagram
- An electrode when polarized frequently yields a current
potential relationship over a region which can be
approximated by:
h=
+-B log (i/io)
where h = change in open circuit potential, i = the current density, B and io
= constants. B is known as the Tafel Slope.
If this behavior is observed a plot of the
semilogarithmic components is known as the Tafel line and
the diagram is called the Tafel diagram.
- tarnish
- Surface discoloration of a metal caused by formation of a
thin film of corrosion product.
- temper
- (1) In heat treatment, to reheat hardened steel or
hardened cast iron to some temperature below the
eutectoid temperature for the purpose of decreasing
hardness and increasing toughness. The process is also
sometimes applied to normalized steel. (2) In tool
steels, temper is sometimes inadvisably used 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 of area during cold working.
- temper color
- A thin, tightly adhering oxide skin (only a few molecules
thick) 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 ultra high-strength steels caused
by tempering in the temperature range of 205C to 400C
(400F to 750F); also called 350C or 500F
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 temperature. Temper
embrittlement can be reversed by re tempering above the
critical temperature range, then cooling rapidly.
- tensile strength
- In tensile testing, the ratio of maximum load to original
cross-sectional area. Also called ultimate tensile
strength.
- tensile stress
- A stress that causes two parts of an elastic body. on
either side of a typical stress plane, to pull apart.
Contrast with compressive stress.
- tension
- The force or load that produces elongation.
- terne
- An alloy of lead containing 3 to l5% Sn, used as a hot
dip coating for steel sheet or plate. Terne coatings,
which are smooth and dull in appearance, give the steel
better corrosion resistance and enhance its ability to be
formed, soldered, or painted.
- 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 embrittlement
- Intergranular fracture of maraging steels with
decreased toughness resulting from improper processing
after hot working. Thermal embrittlement occurs upon
heating above l095C (2000F ) and then slow cooling
through the temperature range of 815C to 980C (1300F to
l800F), and has been attributed to precipitation of
titanium carbides and titanium carbonitrides at austenite
grain boundaries during cooling through the critical
temperature range.
- thermally induced embrittlement
- See embrittlement.
- thermal spraying
- A group of coating or welding processes in which finely
divided metallic or nonmetallic materials are deposited
in a molten or semimolten condition to form a coating.
The coating material may be in the form of powder,
ceramic rod, wire, or molten materials. See also flame
spraying and plasma spraying.
- 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.
- thermogalvanic corrosion
- Corrosion resulting from an electrochemical cell caused
by a thermal gradient.
- threshold stress
- Threshold stress for stress-corrosion-cracking. The
critical gross section stress at the onset of
stress-corrosion cracking under specified conditions.
- throwing power
- (1) The relationship between the current density at a
point on a surface and its distance from the counter
electrode. The greater the ratio of the surface
resistivity shown by the electrode reaction to the volume
resistivity of the electrolyte, the better is the
throwing power of the process. (2) The ability of a
plating solution to produce a uniform metal distribution
on an irregularly shaped cathode. Compare with covering
power.
- tinning
- Coating metal with a very thin layer of molten solder or
brazing filler metal.
- torsion
- A twisting deformation of a solid body about an axis in
which lines that were initially parallel to the axis
become helices.
- torsional stress
- The shear stress on a transverse cross section resulting
from u twisting action.
- total carbon
- The sum of the free carbon and combined carbon (including
carbon in solution) in a ferrous alloy.
- toughness
- The ability of a metal to absorb energy and deform
plastically before fracturing.
- transcrystalline
- See transgranular.
- transcrystalline cracking
- See transgranular cracking.
- transference
- The movement of ions through the electrolyte associated
with the passage of the electric current. Also called
transport or migration.
- 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 metal
- A metal in which the available electron energy levels are
occupied in such away that the d-band contains less than
its maximum number of ten electrons per atom, for
example, iron, cobalt, nickel, and tungsten. The
distinctive properties of the transition metals result
from the incompletely filled d-levels.
- 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. (2) Sometimes used to denote an arbitrarily
defined temperature within a range in which the ductility
changes rapidly with temperature.
- transpassive region
- The region of an anodic polarization curve, noble
to and; above the passive potential range, in
which there is a significant increase in current density
(increased metal dissolution) as the potential becomes
more positive (noble).
- transpassive state
- (1) State of anodically passivated metal characterized by
a considerable increase of the corrosion current, in the;
absence of pitting, when the potential is
increased. (2) The noble region of potential where an
electrode exhibits at higher than passive current
density.
- triaxial stress
- See principal stress (normal).
- tuberculation
- The formation of localized corrosion products
scattered over the surface in the form of knoblike mounds
called tubercles.
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U
- u-bend specimen
- Horseshoe-shaped test piece used to detect the
susceptibility of a material to stress corrosion cracking.
- ultimate strength
- The maximum stress (tensile. compressive, or shear) a
material can sustain without fracture, determined by
dividing maximum load by the original cross-sectional
area of the specimen. Also called nominal strength or
maximum strength.
- underfilm corrosion
- Corrosion that occurs under organic films in the form of
randomly distributed threadlike filaments or spots. In
many cases this is identical to filiform corrosion.
- uniaxial stress
- See principal stress (normal).
- uniform corrosion
- (1) A type of corrosion attack (deterioration) uniformly
distributed over metal surface. (2) Corrosion that
proceeds at approximately the same rate over a metal
surface. Also called general corrosion.
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V
- vacuum deposition
- Condensation of thin metal coatings on the cool surface
of work in vacuum.
- valence
- A positive number that characterizes the combining power
of an element for other elements, as measured by the
number of bonds to other atoms that one atom of the given
element forms upon chemical combination: hydrogen is
assigned valence 1, and the valence is the number of
hydrogen atoms, or their equivalent, with which an atom
of the given element combines.
- vapor deposition
- See chemical vapor deposition, physical vapor
deposition and sputtering.
- vapor plating
- Deposition of a metal or compound on a heated surface by
reduction or decomposition of a volatile compound at a
temperature below the melting points of the deposit and
the base material. The reduction is usually accomplished
by a gaseous reducing agent such as hydrogen. The
decomposition process may involve thermal dissociation or
reaction with the base material. Occasionally used to
designate deposition on cold surfaces by vacuum
evaporation. See also vacuum deposition.
- voids
- A term generally applied to paints to describe holidays,
holes, and skips in a film. Also used to
describe shrinkage in castings and weld.
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W
- wash primer
- A thin, inhibiting paint, usually chromate pigmented with
a polyvinyl butyrate binder.
- weld cracking
- Cracking that occurs in the weld metal. See also cold
cracking, hot cracking, lamellar tearing, and stress-relief
cracking.
- weld decay
- Intergranular corrosion, usually of stainless
steels or certain nickel-base alloys, that occurs as the
result of sensitization in the heat-affected zone
during the welding operation.
- wetting
- A condition in which the interfacial tension between a
liquid and a solid is such that the contact angle is 0
to 90 degrees.
- wetting agent
- A substance that reduces the surface tension of a liquid,
thereby causing it to spread more readily on a solid
surface.
- white liquor
- Cooking liquor from the kraft pulping process produced by
recausticizing green liquor with lime.
- white rust
- Zinc oxide: the powdery product of corrosion of zinc or
zinc-coated surfaces.
- work hardening
- Same as strain hardening.
- working electrode
- The test or specimen electrode in an electrochemical
cell.
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X
No X definitions.
Y
- yield
- Evidence of plastic deformation in structural
materials. Also called plastic flow or creep. See also
flow.
- 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. Only certain metals
- those that exhibit a localized, heterogeneous type of
transition from elastic deformation to plastic
deformation - produce a yield point. If there is a
decrease in stress after yielding, a distinction may be
made between upper and lower yield points. The load at
which a sudden drop in the flow curve occurs is called
the upper yield point. The constant load shown on the
flow curve is the lower yield point.
- yield strength
- The stress at which a material exhibits a specified
deviation from proportionality of stress and strain. An
onset of 0.2% is used for many metals.
- yield stress
- The stress level in a material at or above the yield
strength but below the ultimate strength, i.e.,
a stress in the plastic range.
Back to top
Z
- zeta potential
- See electrokinetic potential.
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