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Abstract

The fundamental principles of crystallization and polymorph selection in metals are largely determined during the early stages of nucleation. The presence of impurities and the crystallization conditions influence directly the microstructural evolution of the material. In this work we investigate the influence of small prestructured seeds on the nucleation mechanism during solidification in nickel. We employ transition path sampling simulations to enable the investigation of nucleation on the atomistic level. The analysis of the transition path ensemble obtained from our simulations indicates that, in comparison to homogeneous nucleation the presence of fcc and hcp seeds enhances the nucleation rate and determines the structure of the growing nuclei. Icosahedral and bcc seeds on the other hand have no effect on either the mechanism or the nucleation rates. Furthermore, we demonstrate that different conditions of undercooling and pressure determine the amount of hcp and fcc coordinated atoms that compose the growing nuclei and therefore the selected polymorph. Our results provide atomistic insight into the process of seeded heterogeneous nucleation at different crystallization conditions and shed light on the principles of polymorph selection in Ni.