Monte Carlo simulation of atomic migration in L12 superstructure

Extensive resistometric investigations indicated that the "order-order" relaxations in Ni3Al are composed of two simultaneous single-exponential processes strongly differing in rates [1]. In order to explain the experimental results Monte Carlo simulations of the processes in L1(2)- ordered A(3)B system have been taken up assuming the Glauber algorithm for vacancy mechanism of atomic jumps. The configuration energy of the system was approximated by an Ising formula involving pair-interactions of atoms in two co-ordination shells. Laplace transformations of the simulated ''order-order'' relaxation curves revealed a domination of two relaxation times tau(1) and tau(s) (usually tau(1) > 10 x tau(s)). The contribution of the fast relaxation process was always higher in the case of ordering than in the case of disordering of the system. It was indicated that the fast relaxation process consists of the creation (disordering) or recombination (ordering) of the nn A- and B-antisite pairs. The slow relaxation process is a highly complex co-operative one, which finally leads to the equilibrium degree of long-range order (LRO) with new distribution of the anti-site atoms.