Ordering kinetics in an fcc A_3B binary alloy model: Monte Carlo studies

TL;DR

This study uses Monte Carlo simulations to explore the ordering kinetics in an fcc A_3B binary alloy model, revealing different ordering behaviors depending on the quench depth and providing insights into physical time scales and domain structures.

Contribution

It introduces a detailed Monte Carlo approach to distinguish ordering scenarios and estimates physical timescales relevant to Cu_3Au alloys.

Findings

Identification of incubation time for ordering after shallow quenches

Observation of spinodal ordering in deep quenches

Slower coarsening than Lifshitz-Allen-Cahn law predicts

Abstract

Using an atom-vacancy exchange algorithm, we investigate the kinetics of the order-disorder transition in an fcc A_3B binary alloy model following a temperature quench from the disordered phase. We observe two clearly distinct ordering scenarios depending on whether the final temperature T_f falls above or below the ordering spinodal T_{sp}, which is deduced from simulations at equilibrium. For shallow quenches (T_f>T_{sp}) we identify an incubation time tau_{inc} which characterizes the onset of ordering through the formation of overcritical ordered nuclei. The algorithm we use together with experimental information on tracer diffusion in Cu_3Au alloys allows us to estimate the physical time scale connected with tau_{inc} in that material. Deep quenches, T_f<T_{sp}, result in spinodal ordering. Coarsening processes at long times proceed substantially slower than predicted by the Lifshitz-Allen-Cahn t^{1/2} law. Structure factors related to the geometry of the two types of domain walls that appear in our model are found to be consistent with Porod's law in one and two dimensions.