Million atom MD simulations of crystal nucleation in supercooled Ni

Reference Presenter Authors
10-063 Luis Gustavo Vieira Gonçalves Gonçalves, L.G.(Universidade Tecnológica Federal do Paraná); Zanotto, E.D.(Federal University of Sao Carlos); The goal of this work was to obtain crucial information about the homogeneous nucleation kinetics in pure supercooled liquids using molecular dynamics simulations. The relevant data includes the critical nucleus size N*, the average times to form the first critical nuclei, t1, and the steady-state nucleation rates, Jst. In this particular study, we used metallic Ni. With the aid of thermodynamic properties obtained from simulations, such as the enthalpy of fusion, the melting temperature, and the interfacial free energy,the nucleation data were analyzed using the Classical Nucleation Theory (CNT). The nucleation rates at three temperatures were calculated by three different methodsfor comparison and consistency tests. For a small system of 40,000 atoms, the mean first-passage time (MFPT) and the direct observation (DO) methods were employed using 600 independent runs for good statistics. We employed the Yasuoka-Matsumoto (YM) method for a large (4 million atoms) system to verify possible size effects on the nucleation parameters. The temperature range in which it was possible to observe nucleation is very narrow for this system, and thus only three temperatures (1180, 1200 and 1210 K) were analyzed. Our results show that the small variation of Ni self-diffusion did not significantly affect the nucleation rates in this temperature range. This implies that, according to CNT, the Gibbs free-energy or the nucleus-liquid surface energy dominated the temperature dependence of Jst. We have also observed that the critical nucleus size is only weakly dependent on the temperature. There is a clear trend showing that the nucleation rates in the large system become smaller than in the small one with increasing temperature, which indicates a system size effect on the nucleation kinetics.
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