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Unformatted text preview: 1 MAE 581 Advanced Materials Science Lecture note 10 Phase equilibrium and structure Principles and applications of phase diagrams The term ‘phase’ refers to a separate and identifiable state of matter in which a given substance may exist. When referring to a particular phase in the structure of a material, we imply a region comprising a large number of atoms (or ions or molecules) and the existence of a bounding surface which separates it from contiguous phases. Local structural disturbances and imperfections are disregarded. Thus, a pure metal or an oxide solid solution are each described, by convention, as single-phase structures even though they may contain grain boundaries, concentration gradients (coring) and microdefects, such as vacancies, dislocations and voids Industrial practice understandably favors relatively rapid cooling rates, frequently causing phases to exist in a metastable condition. Some form of ‘triggering’ process, such as thermal activation, is needed before a metastable phase can adopt the stable, or equilibrium, state of lowest energy...
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- Fall '11
- Thermodynamics, Willard Gibbs, phase rule