Nucleation in Ni-Al alloys: An atomistic study

Yanyan Liang, ICAMS, Ruhr-Universität Bochum, Bochum, Germany
Grisell Díaz Leines, ICAMS, Ruhr-Universität Bochum, Bochum , Germany
Jutta Rogal, ICAMS, Ruhr-Universität Bochum, Bochum, Germany
Ralf Drautz, ICAMS, Ruhr-Universität Bochum, Bochum, Germany

Ni-Al alloys are a basic component of high-temperature superalloys. The crystallization in Ni3Al is of particular interest due to its high strength properties. The initial nucleation is a crucial step in solidification, but atomistic insight into the mechanism in binary alloy still remain elusive due to the extended time scales and the complexity of the process. In this work, we investigate the nucleation in Ni3Al from an atomistic perspective. We employ transition path sampling simulations and generate an ensemble of molecular dynamics trajectories to extract the thermodynamic and kinetic properties. The analysis of path ensemble indicates a strong competition between the structural ordering and the chemical ordering during the nucleation process. As a consequence, the size of the growing nucleus is not sufficient to describe the nucleation mechanism in contrast to what we observed in pure metals. To fully characterize the nucleation process in binary alloys, we need to explicitly consider the interplay between the size as well as the crystal structure of the growing nucleus.

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