Computer simulations of disordering kinetics in irradiated intermetallic compounds

Molecular-dynamics computer simulations of collision cascades in intermetallic ${\mathrm{Cu}}_{3}$Au, ${\mathrm{Ni}}_{3}$Al, and NiAl have been performed to study the nature 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 recovery) of the crystalline order and the evolution of the chemical order, both processes being developed on different time scales. In our previous simulations on ${\mathrm{Ni}}_{3}$Al and ${\mathrm{Cu}}_{3}$Au [T. Diaz de la Rubia, A. Caro, and M. Spacz\'er, Phys. Rev. B 47, 11 483 (1993)] we found a significant difference between the time evolution of the chemical short-range order (SRO) and the crystalline order in the cascade core for both alloys, namely the complete loss of the crystalline structure but only partial chemical disordering. Recent computer simulations in NiAl show the same phenomena. To understand these features we study the liquid phase of these three alloys and present simulation results concerning the dynamical melting of small samples, examining the atomic mobility, the relaxation time, and the saturation value of the chemical short-range order. An analytic model for the time evolution of the SRO is given.