Molecular Dynamics Simulations Of Crystal Growth For Metals

The study of crystal growth has been developed from preparation technology research to producing method and crystal growth theory. They are seeping mutually and promote each other. The study of crystal preparation techniques provides the crystal growth theory so much research resources, and the crystal growth theory reveals the basic law of crystal growth and gives some guidance to preparation techniques. The research of crystal growth mechanism is the basis of the research for metals, and also a hotspot in the research field of the condensed matter physics. Although the study of crystal growth theory has made a great progress, because of the complexity of the crystal growth process and the growth environment, crystal growth theory still needs to be further developed.We use molecular dynamics methods to simulate the crystal growth process of some pure melts and alloys, and analyze the relationship between temperature and crystal growth,and reveals the dynamics mechanism of crystal growth in deeply supercooling. The research of this paper includes:1. We simulate the crystal growth of elemental Cu, Pd, Ta and binary NiAl, CuZr alloys at different temperatures, and calculate their crystal growth velocity. By analyzing the data, we find that the temperature dependence of growth velocity for elemental Cu and Pd is consistent with the prediction of the collision-limited model, where as for NiAl and CuZr alloys obeys the diffusion-limited model. The glass former, CuZr, displays abnormally slow crystal growth compared with elemental Cu, Pd, Ta and poor glass former NiAl. We propose that the density and the structural order layering arose a strong stress layering at the interface, which tends to confine atoms in the near-interface region, forming a slow diffusion zone. The interface layering suppresses the crystal growth. In order to verify the viewpoint above, we simulate the crystal growth of element Cu, Pd and binary CuZr, NiAl alloys under different compression, and analyze the density and stress at the interface, and the crystal growth velocity as compressing, then confirmed the viewpoint above.2. We simulate the growth and melting of embryos with different radius in its liquids.Based on the classical nucleation theory and Gibbs-Thomson model, we calculate the interfacial energy of liquid-solid, and further analyze the thermodynamics and kinetics factors that affect the nucleation rate of binary Ni Al, CuZr alloys. The result shows that the slow nucleation rate of CuZr is mainly induced by the slow diffusion near the interface ofliquid-solid, rather than the interfacial energy.In this paper, through a series of comparative research, we study the ability of crystallization from two aspects: crystal growth and nucleation. We propose a reasonable explanation of the poor crystallization ability of CuZr alloy.