COMPUTER-SIMULATIONS OF DISORDERING KINETICS IN IRRADIATED INTERMETALLIC COMPOUNDS

Molecular-dynamics computer simulations of collision cascades in inter metallic Cu3Au, Ni3Al, and NiAl have been performed to study the natur e of the disordering processes in the collision cascade. The choice of these systems was suggested by the quite accurate description of the thermodynamic properties obtained using embedded-atom-type potentials. Since melting occurs in the core of the cascades, interesting effects appear as a result of the superposition of the loss (and subsequent r ecovery) of the crystalline order and the evolution of the chemical or der, both processes being developed on different time scales. In our p revious simulations on Ni3Al and Cu3Au [T. Diaz de la Rubia, A. Care, and M. Spaczer, Phys. Rev. B 47, 11483 (1993)] we found a significant difference between the time evolution of the chemical short-range orde r (SRO) and the crystalline order in the cascade core for both alloys, namely the complete loss of the crystalline structure but only partia l chemical disordering. Recent computer simulations in NiAl show the s ame phenomena. To understand these features we study the liquid phase of these three alloys and present simulation results concerning the dy namical melting of small samples, examining the atomic mobility, the r elaxation time, and the saturation value of the chemical short-range o rder. An analytic model for the time evolution of the SRO is given.