The kinetic cluster-field method and its application to studies of L1(2)-type orderings in alloys

The earlier-described master equation approach to configurational kinetics of nonequilibrium alloys is applied to study Ll(2)-type orderings in FCC al loys. We describe the kinetic tetrahedron cluster-field method which genera lizes a similar method used for equilibrium systems to the case of non-equi librium alloys. The method developed is used to simulate Al --> Ll(2) and A l --> Al + Ll(2) transformations after a quench of an alloy from the disord ered Al phase to the single-phase Ll(2) state or the two-phase Al + Ll(2) s tate for a number of alloy models with both short-range and long-range inte ractions. Simulations of the Al --> Ll(2) transition show a sharp dependenc e of the microstructural evolution on the type of interaction, and particul arly on the interaction range. The simulations also reveal a number of pecu liar features in both the transient microstructures and the transformation kinetics, many of them agreeing well with experimental observations. Micros tructural evolution under Al --> Al + Ll(2) transition was found to be less sensitive to the type of the finite-range ('chemical') interaction, while in the presence of elastic interaction this evolution shows a number of spe cific features which were earlier discussed phenomenologically by Khachatur yan and co-workers and are illustrated by our simulations. We also consider the problem of the occurrence of a transient congruent ordering under Al - -> Al + Ll(2) transformation and discuss the microstructural features of th is stage.