(See related pages)
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| System | a portion of the universe that has been isolated so that its properties can be studied. (See page(s) 417; Sec. 8.1) |
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| Equilibrium | a system is said to be in equilibrium if no macroscopic changes take place with time. (See page(s) 417; Sec. 8.1) |
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| Phase | a physically homogeneous and distinct portion of a material system. (See page(s) 417; Sec. 8.1) |
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| Equilibrium phase diagram | a graphical representation of the pressures, temperatures, and compositions for which various phases are stable at equilibrium. In materials science the most common phase diagrams involve temperature versus composition. (See page(s) 417; Sec. 8.1) |
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| Gibbs phase rule | the statement that at equilibrium the number of phases plus the degrees of freedom equals the number of components plus 2. P + F = C + 2. In the condensed form with pressure ≈ 1 atm, P + F = C + 1. (See page(s) 417; Sec. 8.2) |
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| Degrees of freedom (F) | the number of variables (temperature, pressure, and composition) that can be changed independently without changing the phase or phases of the system. (See page(s) 417; Sec. 8.2) |
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| Number of components of a phase diagram | the number of elements or compounds that make up the phase-diagram system. For example, the Fe-Fe3C system is a two-component system; the Fe-Ni system is also a two-component system. (See page(s) 417; Sec. 8.2) |
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| Isomorphous system | a phase diagram in which there is only one solid phase; that is, there is only one solid-state structure. (See page(s) 417; Sec. 8.3) |
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| Liquidus | the temperature at which liquid starts to solidify under equilibrium conditions. (See page(s) 417; Sec. 8.3) |
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| Solidus | the temperature during the solidification of an alloy at which the last of the liquid phase solidifies. (See page(s) 418; Sec. 8.3) |
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| Lever rule | the weight percentages of the phases in any two-phase region of a binary phase diagram can be calculated using this rule if equilibrium conditions prevail. To use this rule, one takes the ratio of the segment of the tie line opposite the phase of interest and on the opposite side of the alloy or composition of interest over the whole tie line. (See page(s) 418; Sec. 8.4) |
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| Tie line | a horizontal working line drawn at a particular temperature between two phase boundaries (in a binary phase diagram) to be used to apply the lever rule. Vertical lines are drawn from the intersection of the tie line with the phase boundaries to the horizontal composition line. A vertical line is also drawn from the tie line to the horizontal line at the intersection point of the tie line with the alloy of interest to use the lever rule. (See page(s) 418; Sec. 8.4) |
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| Eutectic reaction (in a binary phase diagram) | a phase transformation in which all the liquid phase transforms on cooling into two solid phases isothermally. (See page(s) 418; Sec. 8.6) |
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| Eutectic temperature | the temperature at which a eutectic reaction takes place. (See page(s) 418; Sec. 8.6) |
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| Eutectic composition | the composition of the liquid phase that reacts to form two new solid phases at the eutectic temperature. (See page(s) 418; Sec. 8.6) |
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| Eutectic point | the point determined by the eutectic composition and temperature. (See page(s) 418; Sec. 8.6) |
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| Invariant reactions | equilibrium phase transformations involving zero degrees of freedom. (See page(s) 418; Sec. 8.6) |
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| Solvus | a phase boundary below the isothermal liquid + proeutectic solid phase boundary and between the terminal solid solution and two-phase regions in a binary eutectic phase diagram. (See page(s) 418; Sec. 8.6) |
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| Hypoeutectic composition | one that is to the left of the eutectic point. (See page(s) 418; Sec. 8.6) |
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| Hypereutectic composition | one that is to the right of the eutectic point. (See page(s) 418; Sec. 8.6) |
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| Proeutectic phase | a phase that forms at a temperature above the eutectic temperature. (See page(s) 418; Sec. 8.6) |
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| Primary phase | a solid phase that forms at a temperature above that of an invariant reaction and is still present after the invariant reaction is completed. (See page(s) 418; Sec. 8.6) |
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| Peritectic reaction (in a binary phase diagram) | a phase transformation in which, upon cooling, a liquid phase combines with a solid phase to produce a new solid phase. (See page(s) 418; Sec. 8.7) |
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| Monotectic reaction (in a binary phase diagram) | a phase transformation in which, upon cooling, a liquid phase transforms into a solid phase and a new liquid phase (of different composition than the first liquid phase). (See page(s) 418; Sec. 8.8) |
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| Terminal phase | a solid solution of one component in another for which one boundary of the phase field is a pure component. (See page(s) 418; Sec. 8.10) |
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| Intermediate phase | a phase whose composition range is between those of the terminal phases. (See page(s) 418; Sec. 8.10) |