The research team of Associate Professor Yasushi Shibata of the Graduate School of Engineering, the University of Tokyo, Associate Professor Tomohiro Takagi of the Department of Mechanical Engineering, Kyoto University of Crafts and Textiles, and Associate Professor Soichi Ohno of the Graduate School of Engineering, Hokkaido University, is a large-scale molecular dynamics research team. By reproducing the process of homogeneous nucleation from pure metal hypercooled melt by method simulation, it was discovered that local heterogeneity develops during homogeneous nucleation.
Nucleation is a phenomenon in which different thermodynamic states such as the formation of local crystals in a liquid appear during the solidification process, and is emphasized in the materials and semiconductor industries.However, it was difficult to observe homogeneous nucleation due to impurities and nucleation from the walls of the vessel in the real world.In the molecular dynamics simulation that tracks the position and velocity of all atoms, there is a limit to the spatiotemporal scale of the computational system because it is necessary to simulate a large number of atoms on a time scale of two states such as liquid and solid.
This time, the research team conducted a molecular dynamics simulation of 2.5 GPUs in parallel on the GPU supercomputer "TSUBAME 512" using a unique molecular dynamics code for GPU.Specifically, a pure iron melt consisting of more than 10 billion atoms was kept in a supercooled state, and the process of nucleation was observed.
As a result, it was found that the local structure of the icosahedron increased in the liquid around the preceding nucleus expressed in the supercooled melt, inducing a large number of satellite nuclei.We also found that another crystal grain with a specific azimuth relationship with a small grain boundary energy forms inhomogeneous nuclei from the surface of some preceding nuclei, and that there is local inhomogeneity even during homogeneous nucleation. Revealed.
The results of this research are said to have been obtained by reproducing the process of the phenomenon at the atomic level, and provide knowledge for improving the actual process of the material.
Paper information: [Nature Communications] Heterogeneity in homogeneous nucleation from billion-atom molecular dynamics simulation of solidification of pure metal
