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phase diagrams is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases; or to show what phases are present in the material system at various T, p, and compositions. “equilibrium” is important: phase diagrams are determined by using slow cooling conditions ⇒ no information about kinetics.
Phase diagrams 1. Free energy curves can be used to determine the most stable state for a system, i.e. the phase or phase mixture with the lowest free energy for a given temperature and composition. Below is a schematic free-energy curve for the solid phase of an alloy.
• Phase diagrams are a road map to understand the conditions for phase formation or transformation in any material system • One can use phase diagrams as the starting point for materials design and process
Many alloys are created by mixing substances in the liquid phase and it is convenient to consider the formation of alloy structures on the basis of the solidification of liquid alloys. Alloy structures and, hence, alloy properties, will depend on the nature of the solid phase or phases formed.
Solid-state reactions differ in two important aspects from liquid reactions in the manner in which they attain the equilibrium conditions predicted by the phase diagram. Solid-state reactions occur much more slowly, are sub-ject to greater undercooling, and rarely attain true equilibrium conditions.
•Phase Diagrams are maps of the equilibrium phases associated with various combinations of temperature, pressure, and composition. •A Phase Diagram is a type of chart used to show conditions at which thermodynamically distinct phases can occur at equilibrium. 2
Important binary phase diagrams involving liquid and solid reactions are covered in Chapter 4 (isomorphous), Chapter 5 (eutectic), Chapter 6 (peritectic), and Chapter 7 (monotectic). Solid-state transformations are covered in Chapter 8 and include the important eutectoid and peritectoid reactions.
