Glossary | T (The vocabulary of the coating and heat-treating industries—explained)

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T

Tellurium (Te)

A chemical element that is added to steel to modify sulfide type inclusion size, morphology and distribution. The resulting sulfide type inclusions are finer and remain ellipsoidal in shape following hot working, thereby improving transverse properties.

Temper

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.
In tool steels, temper is sometimes used, but inadvisably, to denote carbon content.
In nonferrous alloys and in some ferrous alloys, the hardness and strength produced by mechanical and/or thermal treatment and characterized by certain structure, mechanical properties or reduction of area during cold working.

Temper Carbon

The same as annealing carbon.

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.

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 by retempering above the critical temperature range, then cooling rapidly.

Temper Stressing

Quenching in water from the tempering temperature to improve fatigue strength.

Temperature

Degree of warmth or coldness in relation to temperatures upon which temperature scales are based. Accepted scales include Centigrade, Fahrenheit and Kelvin, among others.
Fahrenheit: 32 degrees on the Fahrenheit scale (denoted 32°F) is the temperature at which water freezes, and 180° hotter is the temperature at which water boils.
Celcius: 0 degrees on the Celcius scale (denoted 0°C) is the temperature at which water freezes, and 100° hotter is the temperature at which water boils.
kelvin: 0 on the Kelvin scale (denoted 0 K or 0 kelvin) is the temperature at which all atomic motion ceases, and is equal to -273°C. It uses the same unit increment as the Celcius scale, making the temperature at which water freezes equal to 273 K.

Tempered Martensite Embrittlement

Embrittlement of ultra-high-strength steels caused by tempering in the temperature range 205°C–400°C (400°F–750°F); also called 350°C or 500°F embrittlement. 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.

Tempering

A treatment consisting of heating uniformly to some predetermined temperature under the critical range, holding at that temperature a designated period of time and then cooling in air or liquid. This treatment is used to produce one or more of the following end results: A) to soften material for subsequent machining or cold working, B) to improve ductility and relieve stresses resulting from prior treatment or cold working, and C) to produce the desired mechanical properties or structure in the second step of a double treatment.

Tensile Strength

The maximum stress in uniaxial tension testing which a material will withstand prior to fracture. The ultimate tensile strength is calculated from the maximum load applied during the test divided by the original cross-sectional area. Compare with Yield Strength.

Tensile Stress

Axial forces per unit area applied to a body, tending to extend it.

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 the slope of the plotted 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.

Thermal Barrier Coating

A coating produced to present an insulating barrier to a heat source and to protect the substrate.

Thermal Conductivity

The property of matter by which heat energy is transmitted through particles in contact. For engineering purposes, the amount of heat conducted through refractories is usually given in Btu per hour for one square foot of area, for a temperature difference of one degree Fahrenheit, and for a thickness of one inch (Btu/hr×ft×F/in).

Thermal Diffusion (TD)

A salt bath treatment at about 900°C for high carbon tool steels. Produces a very hard layer of vanadium carbide, typically .0002-.0003” thick. Also called Thermo-Reactive Diffusion (TRD).

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 Fatigue

(1) Fracture resulting from the presence of temperature gradients that vary with time in such a manner as to produce cyclic stresses in a structure.
(2) Failure resulting from rapid cycles of alternate heating and cooling.

Thermal Shock

Stress developed by rapid and uneven heating of a material.

Thermal Spraying

A process in which coating material is heated and accelerated from a spray torch towards the work piece. The deposited material forms a coating on the surface.

Thermal Stresses

Stresses in metal resulting from nonuniform temperature distribution. Usually occurs during the cooling of a part.

Thermochemical Treatment

A 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.

Thermochemically Formed Coatings

A painted, dipped or sprayed chromium-oxide-based coating consolidated by repeated deposition and curing cycles (about 500°C).

Thermo-Reactive Diffusion (TRD)

A salt bath treatment at about 900°C for high-carbon tool steels. Produces a very hard layer of vanadium carbide, typically .0002-.0003” thick. The shortened name of this process is “thermal diffusion” (TD).

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.

Thermography

An NDE technique in which the coating is flash heated and then viewed with an infrared camera. Hot spots indicate areas of poor bonding or greater coating thickness.

Thermomechanical Working

A general term covering a variety of processes combining controlled thermal and deformation treatments to obtain specific properties. Same as thermo-mechanical treatment.

Three-Quarters Hard

A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength and hardness about midway between that of half hard temper and that of full hard temper.

Time Quenching

A term used to describe a quench in which the cooling rate of the part being quenched must be changed abruptly at some time during the cooling cycle.

Time-Temperature-Transformation (TTT) Diagram

See Isothermal Transformation (IT) Diagram.

Titanium (Ti)

A metallic element that is added to boron steels because it combines with oxygen and nitrogen, which increases the effectiveness of boron. Titanium, as titanium nitride, also provides grain size control at elevated temperatures in microalloy steels. In excess, titanium is detrimental to machinability and internal cleanness.

Titanium Nitride (TiN)

Gold colored ceramic, typically applied as a thin coating by either PVD or CVD. Very hard (3500Hv). Used on cutting tools and forming tools and other surfaces requiring wear resistance.

Tolerance

The permissible deviation of a dimension from the nominal or desired value. The minimum clearance between mating parts.

Tool Steel

Any high-carbon or alloy steel used to make a cutting tool for machining and forming metals and for metal-casting Dies.

Total Carbon

The sum of the free and combined carbon (including carbon in solution) in a ferrous alloy.

Total Indicator Reading

See preferred term: total indicator variation.

Total Indicator Variation

The difference between the maximum and minimum indicator readings during a checking cycle.

Toughness

The ability of a metal to absorb energy and deform plastically before fracturing.

Trajectory

The path a particle takes when it is injected into a stream of moving gas (or fluid). It is used in CFD to predict the path of the metal powder used in the plasma spray gun analysis.

Transcrystalline

See transgranular.

Transferred Arc

In a plasma torch, the plasma jet is emitted from the torch, and the current flows from the internal cathode to the internal anode represented by the nozzle of the torch. When the jet is carried to another anode with it being electrically favorable to do so, the current will then transfer to the second anode—usually the work piece—and the arc is said to be transferred.

Transformation Hardening

A heat treatment that is part of of austenitization, and which is followed by cooling under conditions such that the austenite transforms more or less completely into martensite and possibly bainite.

Transformation Ranges

Those ranges of temperature within which a phase forms during heating and transforms during cooling. The two ranges are distinct; sometimes overlapping but never coinciding. The limiting temperatures of the ranges depend on the composition of the alloy and on the rate of change of temperature, particularly during cooling. See transformation temperature.

Transformation Temperature

The temperature at which a change in phase occurs. The term is sometimes used to denote the limiting temperature of a transformation range. The following symbols are used for iron and steels:

Accm – In hypereutectoid steel, the temperature at which the solution of cementite in austenite is completed during heating.

Ac1 – The temperature at which austenite begins to form during heating.

Ac3 – The temperature at which transformation of ferrite to austenite is completed during heating.

Ac4 – The temperature at which austenite transforms to delta ferrite during heating.

Aecm, Ae1, Ae3, Ae4 – The temperature of phase changes at equilibrium.

Arcm – In hypereutectoid steel, the temperature at which precipitation of cementite starts during cooling.

Ar1 – The temperature at which transformation of austenite to ferrite or to ferrite plus cementite is completed during cooling.

Ar3 – The temperature at which austenite begins to transform to ferrite during cooling.

Ar4 – The temperature at which delta ferrite transforms to austenite during cooling.

Ar’ – The temperature at which transformation of austenite to pearlite starts during cooling.

Mf – The temperature at which transformation of austenite to martensite finishes during cooling.

Ms (or Ar”) – The temperature at which transformation of austenite to martensite starts during cooling.

Note: All these changes except the formation of martensite occur at lower temperatures during cooling than during heating, and depend on the rate of change of temperature.

Transformation-Induced Plasticity

A phenomenon, that occurs chiefly in certain highly alloyed steels that have been heat treated to produce metastable austenite and/or martensite, in which on subsequent deformation part of the austenite undergoes strain-induced transformation to martensite. Steels capable of transforming in this manner—commonly referred to as TRIP steels—are highly plastic after heat treatment, but exhibit a very high rate of strain hardening, and thus have high tensile and yield strengths after plastic deformation at temperatures ~20°C–500°C (70°F–930°F). Cooling to -195°C (-320°F) may or may not be required to complete the transformation to martensite. Tempering usually is done following the transformation.

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 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 (e.g. from primarily fibrous [shear] to primarily crystalline [cleavage] fracture). Commonly used definitions are “transition temperature for 50% cleavage fracture”, “10 ft × lbf transition temperature”, and “transition temperature for half maximum energy.”
(2) Sometimes used to denote an arbitrarily defined temperature within a range in which the ductility changes rapidly with temperature.

Transmission Electron Microscopy (TEM)

Applied to thin and thick film analysis, it permits observation of smaller features such as microcolumnar voids and patterns of dislocations in the bulk.

Transparent Electrical Conductors

Include transparent conductive oxide (TCO) films such as indium trioxide (In2O3), tin dioxide (SnO2), zinc oxide (ZnO) and an alloy of indium oxide and tin oxide (ITO). These have numerous applications such as heaters on windows for defrosting, antistatic coatings on display screens, electrodes on flat panel displays and electrochromic devices, and electrodes on both flexible (resistive screen) and rigid (capacitive screen) touch screens. Electrical resistivity for the TCO films can vary from more than 1,000 ohms per “square” to fewer than 10 ohms per square with good optical transmission.

Trap

This condition applies to a wall entity during a CFD analysis of a particulate two-phase flow. A particle touches the wall entity and its momentum and energy are assumed to be completely lost to the wall entity while the mass is assumed to be lost to the fluid.

TRIP (Transformation-Induced Plasticity) Steel

A commercial steel product exhibiting transformation-induced plasticity.

Troostite

(obsolete term!) A previously unresolved, rapidly-etching fine aggregate of carbide and ferrite produced either by tempering martensite at a low temperature or by quenching a steel at a rate slower than the critical cooling rate. Preferred terminology for the first product is tempered martensite; for the latter, fine pearlite.

Tungsten Carbide

A ceramic with metallic coloration that is often applied as a coating, via thermal spraying, with a Co or Ni binder. Used for high-load applications requiring extreme wear resistance.

Tungsten Disulphide

A solid lubricant, stable to 500°C, that is applied at ambient temperature for use at high vacuum, cryogenic or high temperatures. It is 0.5 microns thick. It extends bearing life and prevents galling, fretting and seizing. Can be applied to miniature ball races in assembled condition. It was developed by NASA for use in deep space. It is used in the plastics industry as a permanent release coating.

Turbulent Flow

Technical terminology for the type of flow which occurs when the Reynolds Number exceeds 2000. In contrast to laminar flow, turbulent flow can be described as an irregular and random-looking motion.

Two-Phase

A particular type of analysis where two of the three phases (gas, liquid and solid) are modeled together. The numerical equations are modified to produce an interaction between the two phases.


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