Thermochemical Treatment
Heat treatment carried out in a medium suitably chosen to produce a change in the chemical
composition of the object by exchange with the medium.
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Temper
(1) In heat treatment, reheating hardened steel or hardened cast iron to some temperature below
the eutectoid temperature for the purpose of decreasing hardness and increasing toughness. The
process also is sometimes applied to normalized steel. (2) In tool steels, temper is sometimes
used, but inadvisedly, to denote the 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 in area during cold working.
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Temper Color
A thin, tightly adhering oxide skin 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.
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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.
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Tempered Martensite Embrittlement
Embrittlement of ultrahigh-strength steels caused by tempering in the temperature range of 205 to
400 °C (400 to 750 °F); also called 350 °C or 500 °F 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 prioraustenite
grain boundaries.
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Thermal Analysis
A method for determining transformations in a metal by noting the temperatures at which thermal
arrests occur. These arrests are manifested by changes in slope of the plotted or mechanically
traced heating and cooling curves. When such data are secured under nearly equilibrium
conditions of heating and cooling, the method is commonly used for determining certain critical
temperatures required for the construction of equilibrium diagrams.
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Tantalum Capacitor
A type of electrolytic capacitor that uses tantalum rather than aluminum. The
tantalum can be foil, as is the aluminum in a conventional electrolytic capacitor. It might also take the form of a porous pellet, the irregular surface of which provides a large area in a small volume. An extremely thin oxide layer forms on the tantalum.
These capacitors have high reliability and excellent efficiency, and are used in military applications because they have a low failure rate. They can be used in audio and digital circuits in place of aluminum electrolytic capacitors. The main disadvantage of tantalum capacitors is that they are comparatively expensive. Compare CERAMIC CAPACITOR, ELECTROLYTIC CAPACITOR, MICA CAPACITOR, PAPER CAPACITOR, PLASTIC-FILM CAPACITOR.
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Tee Antenna
An antenna consisting of a horizontal radiator with a vertical lead-in or feeder connected to its center point.
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Telemetric Receiver
A system that selects, amplifies, and demodulates or rectifies a radio signal,
and actuates indicating instruments, recorders, or data processors.
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Telemetric Transmitter
A specialized transmitter that generates radio-frequency (RF) power, adds to it signals delivered by data transducers, and delivers the modulated power to an antenna for transmission to a distant telemetric receiver.
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