Regensburg 2016 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 50: Methods in Computational Materials Modelling II: Microstructure evolution

MM 50.1: Vortrag

Donnerstag, 10. März 2016, 10:15–10:30, H53

Atomistic insight into the structure and shape of growing nuclei during solidification in Ni — •Grisell Diaz Leines, Ralf Drautz, and Jutta Rogal — Atomistic Modelling and Simulation, ICAMS, Ruhr-Universität Bochum, Universitätsstrasse 150, 44801 Bochum, Germany

A crucial stage during solid-liquid phase transformations is the initial nucleation of a stable phase within a metastable medium. Molecular dynamics simulations provide an atomistic picture of solidification, but the modelling of the initial nucleation is hampered by the extended timescale of the process. In this work we employ an advanced computational method, transition path sampling (TPS), to enable the investigation of nucleation in elemental nickel on the atomistic level. We initially focus on homogeneous nucleation. Here, a comparison of the temperature dependence of the free energy barriers to the predictions of classical nucleation theory is discussed. As a second step, we extend our study by including small Ni-clusters as seeds during heterogeneous nucleation. The analysis of the transition path ensemble (TPE) obtained from our simulations indicates the presence of fcc and hcp crystalline structures and nonspherical shapes of the clusters. Furthermore, critical nuclei sizes, free energy barriers and rates, as well as optimal candidates for reaction coordinates based on local structural parameters are identified in the TPE. These results provide fundamental understanding of the nucleation mechanisms and can help to validate and improve existing thermodynamic models describing nucleation in metals.