Kinetics of virtual phase formation during precipitation of ordered intermetallics

The kinetics of structural transformations during precipitation of an ordered phase from a disordered matrix is considered for a prototype binary solid solution in two dimensions. A microscopic kinetic computer simulation technique, which describes simultaneously phase separation, ordering, and coarsening, is employed. It is shown that an ordered phase which does not appear in an equilibrium phase diagram (virtual phase) may temporarily appear at intermediate stages of precipitation. The results are rationalized in terms of thermodynamic stability analysis by taking into account kinetic factors. The structures of antiphase domain boundaries (APB's) are discussed and the role of APB's on the transformation kinetics is emphasized.