6533b86dfe1ef96bd12c9d87

RESEARCH PRODUCT

Spinodal decomposition of a two-dimensional model alloy with mobile vacancies

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Abstract Monte Carlo simulations are performed for the initial stages of phase separation in a model binary alloy (AB), where unmixing is caused by a repulsive energy between atoms of different kind ( e AA = e BB = e ), and a small fraction c v of mobile vacancies is present (typically c v = 0.04.) Unlike previous work, where interdiffusion was modelled in an unrealistic way by direct interchange of A and B atoms for c v = 0, were use the vacancy mechanism of diffusion: A-atoms may jump to vacant sites with a rate Γ A and B-atoms may jump to vacant sites with a rate Γ B , no direct A–B interchange being permitted. It is shown that the overall time-scale on which phase separation proceeds typically is controlled by the slower of these rates, while otherwise there is little dependence of the structure factor S( k , t) on the parameter Γ = Γ B /Γ A ; in fact, S ( k , t) is qualitatively very similar to the direct exchange model, thus justifying the use of the latter. We also observe a slight anisotropy of S ( k , t) for different directions of the scattering vector k . No significant enrichment of the vacancies in the A–B-interfacial regions is observed. Finally, the decrease of the critical temperature with increasing vacancy content is also studied.