Mechanism of 'Order-Order' Kinetics in L1~2 Superstructure Studied by Computer Simulation

摘要

Monte Carlo simulations of the isothermal long-range order (LRO) relaxation in A_3B system with L1_2 superstructure have been performed within a model based o na vacancy jump mechanism between nearest neighbour lattice sites. The studies aimed at the explanation of the origin of two simultaneous LRO relaxation processes experimentally observed in Ni_3Al. An effect of pair interactio nenergies and saddle-point energies (assigned to jumping atoms0 was studied. The preference of vacnacies for the A-sublattice (face centres), commonly postulated for Ni_3Al, occurred only for a narrow range of pair-interaction eneriges within the domain corresponding to L1_2 ordering. It was found that the appearance of the fast relaxation process is definitely correlated with the efficiency of B-atom jumps, as well as with the values of the saddle-point energies. The results lead to a microscopic model of the "order-order" relaxation in L1_2 superstructure and yield new indications for the choice of pair-interaction energy parameters applied in Monte Carlo simulations of atomci migration in L1_2 intermetallic compounds.