Diffusion phase transitions in alloys

We present a critical analysis of research on the thermodynamics, kinetics, and morphology of diffusion phase transitions in alloys. We show that diffusion phase transitions are mainly driven by the chemical potential difference due to a change in the sign of the chemical interaction among the component atoms. We explain how the sign of the chemical interaction energy can be obtained from experimental measurements. Examples are given to illustrate the kinetics and morphology of the ordering separation phase transition in Ni- and Co-based alloys. We show how introducing the concept of the ordering separation phase transition may affect our thinking in this area.