Kinetic features of phase separation under alloy ordering

The microscopic mean-field kinetic equation (MFKE) proposed earlier is used to investigate the kinetics of alloy decomposition in the presence of alloy ordering. A strong interaction between order and concentration fields results in a number of peculiarities in microstructural evolution. The kinetics of spinodal decomposition in ordered alloys has a number of distinct features as compared to disordered alloys; in particular, the amplification factor of the unstable composition fluctuations increases as the distance to the ordering spinodal rather than as the square of the distance to the usual spinodal for disordered alloys. Microstructural evolution is studied using computer simulations based on the MFKE. A great variability of transient microstructures as well as a high sensitivity of the type of evolution to alloy composition, annealing temperature and thermal history has been found. We describe a peculiar kinetic phenomenon which occurs in the regime of spinodal decomposition with ordering: Antiphase boundaries ``replicate,'' generating approximately periodic patterns. We discuss available experimental indications for this replication of antiphase boundaries. {} 1996 The American Physical Society.