Phase diagrams of bcc alloys at low temperatures with ballistic atom movements

Kinetic Monte Carlo simulations were used to determine the steady states of equiatomic bcc alloys with first- and second-nearest-neighbor (1NN and 2NN) effective pair interactions. Atom movements occurred with a vacancy mechanism, and were of two types: thermal and ballistic. The phase diagram in the space spanned by the 1NN and 2NN interaction strengths was determined for thermal atom movements alone, and with some ballistic atom movements. With increasing temperature, the region of B32 phase receded against the adjacent regions of B2 order and unmixed states. With some ballistic atom movements, however, the region of B32 order encroached on the adjacent regions of B2 order and unmixed state. The shifts in phase boundaries are attributed to differences in how the internal energies of the different phases are affected by ballistic atom movements. Local fluctuations in the internal energy density in the presence of ballistic atom movements caused two-phase regions in the phase diagram