NON-INTUITIVE FEATURES OF DISORDER-]ORDER TRANSFORMATIONS

Vacancy-mediated kinetics of chemical disorder --> order transformations in highly non-equilibrium alloys have features that belie conventional intuition. Activated state rate theories have been developed for these disorder --> order kinetics. Some such theories of increasing complexity are presented, and they illustrate how with greater complexity comes a greater ability to control the kinetics of the ordering process in intelligent ways. In addition to the absolute rates of ordering, it is also informative to study the "kinetic paths" of ordering, where the state of the alloy is presented in a two-dimensional plot of one-order parameter against a second-order parameter. The area in this plot that is accessible to the alloy gives an idea of how much control we have in obtaining different non-equilibrium states of the material. Especially for ternary alloys, these kinetic paths can be widely varied, and their shapes can be highly non-intuitive.