Computer simulation of long-range order relaxation in homogeneous systems

The results of previous extensive experiments on gamma'-Ni3Al systems are interpreted and explained by means of Monte Carlo computer simulations. The complex character of the experimental 'order-order' relaxation curves, as well as the theoretically predicted effect of vacancy ordering have been reproduced and analysed in detail in terms of the dynamics of particular kinds of atomic jumps. The Monte Carlo simulations of 'order-order' kinetics were performed both for an Ising A(3)B L1(2)-ordered system and for Ni3Al with lattice energetics considered within the 'embedded-atom-method' (EAM). The EAM yielded estimations of both atomic pair-interactions and 'effective' saddle-point energies for vacancy jumps in Ni3Al. The proposed model scenario for the creation and elimination of anti-site atoms in the relaxing L1(2)-type superstructure shows that the experimentally observed features of the 'order-order' processes in Ni3Al follow from an interplay between short- and long-range ordering effects resulting from the system energetics and the superlattice geometry. (C) 2002 Elsevier Science B.V. All rights reserved.