Suppression of homogeneous crystal nucleation of the NiAl intermetallic by a composition gradient: A molecular dynamics study

Molecular dynamics simulations of homogeneous nucleation of the NiAl intermetallic phase from a liquid solution on cooling indicate that this phase transformation is suppressed in the presence of a composition gradient. A simulation method is designed to generate a sustaining composition gradient at the interface between two materials. As the composition gradient increases, the nucleation energy barrier rises, the critical nucleus size increases, and the nucleus shape develops an increasing asymmetry. A polymorphic nucleation model for a disk-shaped nucleus that incorporates the composition dependence of interfacial free energies was observed to describe the atomic-scale details of the simulation well. Critical nuclei shapes and volumes predicted by the model match with those appearing in the molecular dynamics simulations.