Atomistic Monte Carlo simulations were made of precipitation and B2 ordering, on the body-centered cubic lattice of a binary alloy, by using a vacancy mechanism. These simulations reproduced various experimental observations for a composition that was close to the A2 solubility limit. For example, precipitation and ordering proceeded simultaneously and led to the coarsening of B2 precipitates. At higher solute concentrations, rapid short-range ordering occurred before the A2 phase appeared via the thickening of antiphase boundaries. Nucleation of the A2 phase within B2 domains was also observed, when closer to the B2 solubility limit. The very early stages of ordering were strongly dependent upon atomic mobility parameters. Depending upon the relative exchange frequency of vacancies with A and B atoms, and depending upon the composition, 2 extreme regimes of ordering were identified which could lead to either localized or delocalized ordering.

M.Athènes, P.Bellon, G.Martin, F.Haider: Acta Materialia, 1996, 44[12], 4739-48