Molecular Dynamics Simulation On The Thermodynamic Behaviors Of Metallic Melt And Metallic Glass

The present situations and developments on nanotechnology, metallic melt and metallic glass are briefly reviewed in this thesis. Molecular dynamics simulation method is introduced to investigate the thermodynamic properties of materials at nanoscale. Bulk melting, surface melting and surface premelting behaviors of crystal copper, the formation and microstructure of metallic glass copper and amorphous Ti-Al alloy, and the stress-induced crystallization of the pure metallic glass and amorphous alloy are studied with molecular dynamics simulation of embedded atom method. The unique thermodynamic behaviors of metallic melt and metallic glass are analyzed, and the atomistic mechanisms are discussed.The methodology of simulating the thermodynamic behaviors of solid materials by molecular dynamics method is elucidated in detail. Some key techniques, such as the control of temperature and stress, potential functions are emphasized.Molecular dynamics simulations are carried out to investigate bulk melting and surface melting behaviors of crystal copper. The different mechanisms of bulk melting and surface melting induce the thermal melting point lower than the bulking melting point. Surface melting is dominant in real melting process, so the experimental datum measured is the thermal melting point. Kinetic coefficient is defined as the ratio of the interface velocity to undercooling. The values of low index surfaces [100], [110], [111] are obviously anisotropic.The strain effects on premelting process of copper are performed by atomistic simulation. The observed order in the surface stability follows the order in the packing density. The surfaces of [110] and [100] premelt below but close to the melting point, while the [111] surfaces shows superheating effect. The thickness of quasi-liquid film grows with temperature in surface premelting. The increase of solid free energy induced by strain is the main factor that decreases surface thermal stability. The direction of strain relative to the surface stress also affects the surface premelting process.The rapid solidification of copper and Ti-Al alloy are studied with molecular dynamics to obtain the crystallization and glass formation. The system transforms to the FCC crystallization with relative slow cooling rate, while the glass transition is performed with relatively rapid cooling rate. The results show that metallic glass has higher internal energy and bigger volume compared with crystal. The intrinsic stress field is induced by the distortion of lattice. There are transformations from a metastable crystal phase to a more stable crystal phase at high temperature, while the amorphous keeps stable at room temperature.The stress-induced crystallization behaviors of metallic glass copper are studied. In the tension deformation, the stress overshoots at the initial stage and the steady state stress increases as the applied strain rate increases. The metallic glass transforms to the crystallization at relatively low strain rate, while it keeps amorphous at relatively high strain rate. There are more nanocrystals as the strain rate decrease. In the indentation process, the crystal nucleation, grain growth, and grain coarsening...