Materials Science Glossary - T

temper designation. A letter–digit code used to designate the mechanical and/or thermal treatment to which a metal alloy has been subjected. 

tempered martensite. The microstructural product resulting from a tempering heat treatment of a martensitic steel. The microstructure consists of extremely small and uniformly dispersed cementite particles embedded within a continuous

ferrite or relaxed martensite matrix. Toughness and ductility are enhanced significantlyby tempering. High temperature tempering can lead to confined (locaö) austenite reversion which can profoundly enhance the materials ductility.

tensile strength (TS). The maximum engineering stress, in tension, that may be sustained without catastrophic fracture, i.e. failure. Often termed ultimate (tensile) strength or UTS.

terminal solid solution. A solid solution that exists over a composition range extending to either composition extremity of a binary phase diagram.

tetrahedral position. The void space among close-packed, hardsphere atoms or ions for which there are four nearest neighbors.

thermal conductivity (k). For steady-state heat flow, the proportionality constant between the heat flux and the temperature gradient. Also, a parameter characterizing the ability of a material to conduct heat.

thermal expansion coefficient, linear ( l). The fractional change in length divided by the change in temperature.

thermal fatigue. A type of fatigue failure wherein the cyclic stresses are introduced by fluctuating thermal stresses.

thermally activated transformation. A reaction that depends on atomic thermal fluctuations; the atoms having energies greater than an activation energy will spontaneously react or transform.

thermal shock. The fracture of a brittle material as a result of stresses that are introduced by a rapid temperature change.

thermal stress. A residual stress introduced within a body resulting from a change in temperature.

thermal tempering. Increasing the strength of a glass piece by the introduction of residual compressive stresses within the outer surface using an appropriate heat treatment.

thermoplastic elastomer (TPE). A copolymeric material that exhibits elastomeric behavior yet is thermoplastic in nature. At the ambient temperature, domains of one repeat unit type form at molecular chain ends that crystallize to act as physical crosslinks.

thermoplastic (polymer). A semicrystalline polymeric material that softens when heated and hardens upon cooling.While in the softened state, articles may be formed by molding or extrusion.

thermosetting (polymer). A polymeric material that, once having been cured (or hardened) by a chemical reaction, will not soften or melt when subsequently heated.

tie line. A horizontal line constructed across a two-phase region of a binary phase diagram; its intersections with the phase boundaries on either end represent the equilibrium compositions of the respective phases at the temperature in question.

time–temperature–transformation (T–T–T) diagram. See isothermal transformation diagram.

toughness. A mechanical characteristic that may be expressed in three contexts: (1) the measure of a material’s resistance to fracture when a crack (or other stress-concentrating defect) is present; (2) the ability of a material to absorb energy and plastically deform before fracturing; and (3) the total area under the material’s tensile engineering stress–strain curve taken to

fracture.

trans. For polymers, a prefix denoting a type of molecular structure. For some unsaturated carbon chain atoms within a repeat unit, a single side atom or group may be situated on one side of the double bond, or directly opposite at a 180_

rotation position. In a trans structure, two such side groups within the same repeat unit reside on opposite sides (e.g., trans-isoprene).

transformation rate. The reciprocal of the time necessary for a reaction to proceed halfway to its completion.

transgranular fracture. Fracture of polycrystalline materials by crack propagation through the grains.

translucent. Having the property of transmitting light only diffusely; objects viewed through a translucent medium are not clearly distinguishable.

transmission electron microscope (TEM). A microscope that produces an image by using electron beams that are transmitted (pass through) the specimen. Examination of internal features at high magnifications is possible.

transparent. Having the property of transmitting light with relatively little absorption, reflection, and scattering, so that objects viewed through a transparent medium can be distinguished readily.

transverse direction. A direction that crosses (usually perpendicularly) the longitudinal or lengthwise direction.

trifunctional. Designating monomers that may react to form three covalent bonds with other monomers.

TRIPLEX steels Weight reduced steels containing high amounts of manganese (Mn), aluminium (Al) and carbon (C) are sometimes also referred to as “Triplex” steels.These materials have low mass density (due to high Al content), high strength and excellent ductility in comparison with established steels for structural engineering applications. This attractive property profile derives from an austenitic or austenitic/ ferritic matrix, both stabilized and strengthened by alloying iron (Fe) with Mn (18–28 wt.%) and C (0.7–1.2 wt.%), together with Al addition (3–12 wt.%) for low specific weight and improved corrosion resistance. Profound changes in the mechanical properties can be achieved by ageing the material after solution annealing and quenching. More specifically, kappa-Al(Fe,Mn)3C carbides were found to precipitate from the matrix during ageing, growing from C-enriched areas, most probably formed via spinodal decomposition during quenching. The development of Fe–Mn–Al–C alloys involves simultaneous investigation of the respective microstructural microstructural phenomena by high resolution characterisation techniques such as atom probe tomography (APT) and transmission electron microscopy (TEM).

true strain (_T). The natural logarithm of the ratio of instantaneous gauge length to original gauge length of a specimen being deformed by a uniaxial force.

true stress ( T). The instantaneous applied load divided by the instantaneous cross-sectional area of a specimen.

TWIP steel.  TWIP steels, which stand for twinning-induced plasticity steels, have received very high interest in recent years due to their excellent mechanical properties at room temperature combining high strength (ultimate tensile strength of up to 1 GPa ) and ductility (elongation to fracture up to 100 %) based on a high work-hardening capacity. TWIP steels are austenitic steels, i.e. face-centered cubic (fcc) metallic alloys, with high content in Mn (above 20% in weight %) and small additions of elements such C (<1 wt.%), Si (<3 wt.%), or Al (<3 wt.%). The steels have low stacking fault energy (between 20 and 40 mJ/m2) at room temperature. The high strain-hardening of TWIP steels is commonly attributed to the reduction of the dislocation mean free path with the increasing fraction of deformation twins as these are considered to be strong obstacles to dislocation glide.