Simulation of Early-stage Clustering in Ternary Metal Alloys Using the Phase Field Crystal Method

Phase field crystal methodology is applied, for the first time, to study the effect of alloy composition on the clustering behavior of a quenched/aged supersaturated ternary Al alloy system. An analysis of the work of formation is built upon the methodology developed in Fallah {\it et al.} to describe the dislocation-mediated formation mechanisms of early clusters in binary alloys [Phys. Rev. B., DOI: 10.1103/PhysRevB.00.004100]. Consistent with the experiments, we demonstrate that the addition of Mg to an Al-1.1Cu alloy increases the nucleation rate of clusters in the quenched/aged state by increasing the effective driving force for nucleation, enhancing the dislocation stress relaxation and decreasing the surface energy associated with the Cu-rich Cu-Mg co-clusters. Furthermore, we show that it is thermodynamically favourable for small sub-critical clusters to have higher affinity for Mg than larger overcritical Cu-rich clusters, particularly depicting a two-stage clustering phenomenon.