Term
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Definition
| A strengthening mechanism that relies on a sequence of solid-state phase transformations in generating a dispersion of ultrafine particles of a second phase. Same as precipitation hardening. A form of dispersion strengthening. |
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Definition
| In the context of metallic material, this is a heat treatment used to eliminate part or all of the effects of cold working. For glasses, this is a heat treatment that removes thermally induced stress. |
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Definition
| Reheating a solution-treated and quenched alloy to a temperature below the solvus in order to provide the thermal energy required for a precipitate to form. |
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Definition
| The name given to the FCC crystal structure of iron and iron-carbon alloys. |
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Definition
| A two-phase microconstituent, containing ferrite and cementite, that forms in steels that are isothermally transformed at relatively low temperatures. |
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Definition
| A region of small, randomly oriented grains that forms at the surface of a casting as a result of heterogeneous nucleation. |
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Definition
| A precipitate whose crystal structure and atomic arrangement have a continuous relationship with the matrix from which the precipitate is formed. This provides excellent disruption of the atomic arrangement in the matrix and provides excellent strengthening. |
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Definition
| Deformation of a metal below the recrystallization temperature. During this, the number of dislocations increases, causing the metal to be strengthened as its shape is changed. |
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Definition
| A region of elongated grains having a preferred orientation that forms as a result of competitive growth during the solidification of a casting. |
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Definition
| The minimum size that must be formed by atoms clustering together in the liquid before the solid particle is stable and begins to grow. |
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Definition
| The treelike structure of the solid that grows when an undercooled liquid solidifies. |
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Definition
| Increase in strength of a metallic material by generating resistance to a dislocation motion by the introduction of small clusters of a second material. (second phase strengthening) |
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Definition
| A tiny particle of solid that forms from the liquid as atoms cluster together. This may grow into a stable nucleus or redissolve. |
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Definition
| A three-phase invariant reaction in which one liquid phase solidifies to produce two solid phases. |
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Term
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Definition
| A three phase invariant reaction in which one solid phase transforms to two different solid phases. |
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Definition
| A pinned dislocation that, under an applied stress, produces additional dislocations. This mechanism is at least partly responsible for strain hardening. |
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Term
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Definition
| The temperature difference between the liquidus and solidus temperatures. |
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Term
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Definition
| The physical process by which a new phase increases in size. In the case of solidification, this refers to the formation of a stable solid as the liquid freezes. |
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Term
| Guinier-Preston (GP) zones |
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Definition
| Tiny clusters of atoms that precipitate from the matrix in the early stages of the age-hardening process. Although these zones are coherent with the matrix, they are too small to provide optimum strengthening. |
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Term
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Definition
| Formation of a critically-sized solid from the liquid on an impurity surface. |
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Definition
| Formation of a critically-sized solid from the liquid by the clustering together of a large number of atoms at a high indercooling (without an external interface) |
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Term
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Definition
| Deformation of a metal above the recrystallization temperature. Duing this, only the shape of the metal changes; the strength remains relatively unchanged because no strain hardening occurs. |
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Definition
| The conditions that an alloy or ceramic system must meet if the system is to display unlimited solid solubility. These are necessary, but are not sufficient for materials to show unlimited solid solubility. |
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Definition
| An alloy composition between that of the right-hand-side end of the tie line defining the eutectic reaction and the eutectic composition (more than). |
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Term
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Definition
| An alloy composition between that of the left-hand-side end of the tie line defining the eutectic reaction and the eutectic composition (less than). |
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Term
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Definition
| The addition of heterogeneous nuclei in a controlled manner to increase the number of grains in a casting. |
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Term
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Definition
| A compound formed of two or more metals that has its own unique composition, structure and properties. |
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Term
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Definition
| Diffusion of small atoms in opposite directions. Interdiffusion may eventually produce an equilibrium concentration of atoms within the material. |
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Term
| Isomorphous phase diagram |
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Definition
| A phase diagram in which components display unlimited solid solubility. |
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Term
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Definition
| A technique for determining the amount of each phase in a two phase system. |
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Term
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Definition
| When only a maximum amount of a solute material can be dissolved in a solvent material. |
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Term
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Definition
| Curves on phase diagrams that describe the liquidus temperatures of all possible alloys |
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Definition
| A metastable phase formed in steel and other materials by a diffusionless, athermal transformation |
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Term
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Definition
| The continuous solid phase in a complex microstructure. Solid dispersed phase particles may form within the matrix |
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Term
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Definition
| A region in a phase diagram in which wo phases, with essentially the same structure, do not mix, or have solubility in one another. |
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Definition
| A three-phase reaction in which one liquid transforms to a solid and a second liquid on cooling |
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Term
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Definition
| When a coherent precipitate forms from a solution treated and quenched agehardenable at room temperature, providing optimum strengthening |
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Term
| Nonstoichiometric Intermetallic |
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Definition
| A phase formed by the combination of two components into a compound having a structure and properties different from either component. This has a variable ratio of the components present in the compound. |
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Term
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Definition
| The physical process by which a new phase is produced in a material. In the case of solidification, this refers to the formation of a tiny, stable solid particles in the liquid. |
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Term
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Definition
| A two phase lamellar microconstituent, containing ferrite and cementite, that forms in steels cooled in a normal fashion or isothermally transformed at relatively high temperatures |
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Term
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Definition
| A three phase reaction in which a solid and a liquid combine to produce a second solid on cooling |
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Term
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Definition
| A three phase reaction by which two solids combine to form a third solid on cooling |
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Term
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Definition
| Any portion, including the whole of a system, which is physically homogeneous within it and bounded by a surface so that it is mechanically separable from any other portion. |
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Term
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Definition
| Diagrams showing phases present under equilibrium condition and the phase composition at each combination of temperature and overall composition. Sometimes these also indicate metastable phases. |
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Term
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Definition
| The growth of a smooth solid-liquid interface during solidification, when no undercooling of the liquid is present. |
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Term
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Definition
| A subgrain structure produced in the early stages of annealing. The sub-grain boundaries are a network of dislocations rearranged during heating. |
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Term
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Definition
| Temperature at which the liquid is poured into the mold. |
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Term
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Definition
| A solid phase that forms from the original matrix phase when the solubility limit is exceeded. We often use this term, as opposed to dispersed phase particles, for alloys fomred by precipitation or age hardening. In most cases, we try to control the formation of this second phase particles to produce the optimum dispersion strengthening or age hardening . |
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Term
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Definition
| The microconstituent that forms before the start of a three phase reaction |
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Term
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Definition
| A rapid cooling technique that hardens most steels |
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Term
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Definition
| A low temperature annealing heat treatment designed to eliminate residual stresses introduced during deformation without reducing the strength of the cold-worked material. This is the same as a stress-relief anneal |
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Term
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Definition
| A medium temperature annealing heat treatment designed to eliminate all of the effects of the strain hardening produced during cold working. |
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Term
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Definition
| Stresses introduced in a material during processing. These can originate as a result of cold working or differential thermal expansion and contraction. A stress-relief anneal in metallic materials and the annealing of glasses minimize these. Compressive residual stresses deliberately introduced on the surface by the tempering of glasses or shot peening of metallic materials improve mechanical prperties |
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Term
| Secondary Dendrite Arm Spacing |
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Definition
| The distance between the centers of 2 adjacent secondary dendrite arms |
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Term
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Definition
| The random movement of atoms within an essentially pure material. No net change in composition results. |
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Term
| Solid solution strengthening |
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Definition
| Increasing the strength of a metallic material via the formation of a solid solution |
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Term
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Definition
| Curves on a phase diagram that describe the solidus temperatures of all possible alloys. |
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Term
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Definition
| The amount of one material that will completely dissolve in a second material without creating a second phase |
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Term
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Definition
| The first step in the age hardening heat treatment. The alloy is heated above the solvus temperature to dissolve any second phase and to produce a homogeneous single-phase structure. |
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Term
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Definition
| A solubility curve that separates a single solid phase region from a two-solid phase region in the phase diagram. (also called the proeutectic microconstituent) |
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Term
| Stoichiometric Intermetallic |
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Definition
| A phase formed by the combination of two components into a compound having a structure and properties different from either component. This has a fixed ratio of the components present in the compound |
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Term
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Definition
| Strengthening of a material by increasing the number of dislocations by deformation, or cold working. Also called work hardening. |
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Term
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Definition
| The recovery stage of the annealing heat treatment during which residual stresses are relieved without reducing the mechanical properties of the material. |
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Term
| Supersaturated solid solution |
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Definition
| The solid solution formed when a material is rapidly cooled from a high temperature single phase region to a low temperature two phase region without the second phase precipitating. Because the quenched phase contains no more alloying element than the solubility limit, it is supersaturated in that element |
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Term
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Definition
| A low temperature heat treatment used to reduce the hardness of martensite by permitting the martensite to begin to decompose to the equilibrium phases. This leads to increased toughness |
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Term
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Definition
| A phase diagram for systems consisting of three components |
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Term
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Definition
| A plateau on the cooling curve during the solidification of a material caused by the evolution of the latent heat of fusion during solidification. This heat generation balances the heat being lost as a result of cooling |
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Term
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Definition
| A horizontal line drawn in a two phase of a phase diagram to assist in determining the compositions of the two phases |
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Term
| Total Solidification Time |
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Definition
| The time required for the casting to solidify completely after the casting has been poured. |
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Term
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Definition
| This describes the time required at any temperature for a phase transformation to begin and end. This assumes that the temperature is constant during transformation. |
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Term
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Definition
| A phase diagram in which there is only one component |
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Term
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Definition
| The temperature to which the liquid metal must cool below the equilibrium freezing temperature before nucleation occurs |
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Term
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Definition
| When the amount of one material that will dissolve in a second material without creating a second phase is unlimited |
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Term
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Definition
| Strengthening of a material by increasing the number of dislocations by deformation, or cold working. Also known as strain hardening. |
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