Phase: domain with uniform physical and chemical characteristics (i.e. a homogeneous portion of a system).
Binary phase diagrams: represent the relationships between temperature, composition and quantities of phases (whilst pressure remains constant). These diagrams aid in the prediction of phase transformations and the resulting microstructures.
Homogenous: comprises of a single-phase system.
Heterogenous: comprises of two or more different phases (a multiphase system). In heterogenous systems, each phase has distinct properties and there will be an abrupt change in these at a boundary that separates the phases.
Solvent: element/compound present in the greatest quantity.
Solute: impurity elements.
Solid solution: solution consisting of at least two different atoms. The solute atoms either occupy interstitial or substitutional positions in the solvent lattice while the solvent's crystal structure is maintained.
Solubility limit: the maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution. It occurs at a specific temperature.
Liquidus temperature: specifies temperature above which the material is completely liquid.
Solidus temperature: specifies temperature below which the material is completely solid.
Single phase region: area where the composition of this phase is the same as the overall composition of the alloy.
Eutectic reaction: occurs during cooling, from a liquid phase into two solid phases.
Eutectoid reaction: occurs from one solid phase to two new solid phases.
Peritectic reaction: occurs from a solid and liquid phase to a new solid phase.
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