Monte Carlo simulation of ordering transformations in Ni-Mo-based alloys

The quenched in state of short range order (SRO) in binary Ni-Mo alloys is characterized by intensity maxima at {1 1/2 0} and equivalent positions in the reciprocal space. Ternary addition of a small amount of Al to the binary alloy, on the other hand, leads to a state of SRO that gives rise to intensity maxima at {1 0 0} and equivalent, in addition to {1 1/2 0} and equivalent, positions in the selected area electron diffraction patterns. Different geometric patterns of streaks of diffuse intensity, joining the SRO maxima with the superlattice positions of the emerging long range ordered (LRO) structures or in some cases between the superlattice positions of different LRO structures, are observed during the SRO-to-LRO transitions in the Ni-Mo-based and other 1 1/2 0 alloys. Monte Carlo simulations have been carried out here in order to shed some light on the atomic structures of the SRO and the SRO-to-LRO transition states in these alloys. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.