The master equation approach to configurational kinetics of alloys via the vacancy exchange mechanism: general relations and features of microstructural evolution

The earlier-suggested generalized Gibbs distribution approach to the configurational kinetics of non-equilibrium alloys is extended to the case of many-component alloys and the realistic vacancy-mediated atomic exchange mechanism is incorporated. Exact and approximate equations for the temporal evolution of atomic distributions as well as for the free energy of a non-equilibrium alloy are presented. It is shown that the evolution of the main alloy component distribution for the nearest-neighbour vacancy exchange model can usually be described in terms of an equivalent direct exchange model. This conclusion is illustrated with the computer simulation of decomposition and ordering via the vacancy exchange mechanism for a two-dimensional alloy model. The simulation also reveals the localized ordering phenomenon at very early stages of ordering, in agreement with previous experiments and Monte Carlo simulation, but with no interfacial vacancy trapping which was suggested in previous works in order to explain this phenomenon.