Berlin 2018 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 47: Poster Session II
MM 47.7: Poster
Wednesday, March 14, 2018, 18:30–19:45, Poster C
Nucleation in Ni-Al alloys: An atomistic study — •Yanyan Liang, Grisell Díaz Leines, Jutta Rogal, and Ralf Drautz — Interdisciplinary Center for Advanced Materials Simulation, Ruhr-Universität Bochum, Germany
Ni-Al alloys are a basic component of high-temperature superalloys, the ordered L12 phase in Ni3Al is of particular interest. Nucleation is a crucial step in solidification, but atomistic insight still remains elusive due to the extended time scale and complexity of the nucleation process in binary alloys. We investigate the nucleation in Ni3Al on the atomic scale. We employ transition path sampling and generate an ensemble of molecular dynamics trajectories to extract thermodynamic and kinetic properties, such as nucleation rates and free energies. A strong competition between fcc, hcp and bcc in the growing nucleus predetermines the final dominant polymorphs in the crystallization. In particular, we find that the composition of the growing nucleus remains constant while there is a decreased short-range chemical order in the nuclei. The size of the growing nucleus alone is not a complete reaction coordinate for the nucleation process, in contrast to what we observed in elemental metals. A multi-dimensional description is needed to fully characterize the nucleation process in binary alloys.