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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 ultrahigh-strength steels caused by tempering
in the temperature range of 205 to 400 ºC (400 to 750 ºF); also
called 350 ºC or 500 ºF 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 retempering 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.
therdermal 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 l095 ºC (2000 ºF ) and then slow cooling through the temperature range
of 815 to 980 ºC (1300 to l800 ºF), 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.
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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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