Simulation Study On Evolution Of Microstructures During Solidification Process Of Liquid Metal Zinc

In this thesis, the rapid solidification processes of liquid metal Zn have been simulated at different size and cooling rate,using molecular dynamics method. Adopting the pair distribution function, Honeycutt-Andersen (H-A) bond-type index method, the cluster-type index method (CTIM-2) and the microscopic visualization method, the evolutions of microstructures during the rapid solidification have been analyzed in different aspects.At first, the solidification processes of liquid metal Zn system with 1000 atoms have been simulated at two cooling rates to obtain amorphous and crystal structures respectively, and the differences of microstructures between the amorphous and crystal structure formed at different cooling rates have been investegated. It is found that: when the liquid metal Zn is solidified at the rapid cooling rate, the amorphous structures are formed mainly with the 1551, 1541 and 1431 bond-types; when the liquid metal Zn system is solidified at slower cooling rate, the crystal structures are formed mainly with the 1421 and 1422 bond-types by coexisting of the fcc and hcp basic clusters.At the same time, there are also certain percentage of the 1311 bond-type. In the crystal structure, the fcc and hcp clusters are arranged in layer separately.The multi-layered fcc clusters are nested and linked through the double- layered hcp clusters.Thus the crystal structure with a high level of crystallization is formed.Then, a simulation study has been performed on the effects of four cooling rates on microstructure during the solidification of liquid metal Zn.It has been found that the crystallizaion temperature Tc enhances with the decrease of cooling rate. At the same time, it is found that the effects of cooling rates on the average atomic energy and the microstructure of system show a non-linear relationship. The reason for this result may be due to the size effect.In order to reduce the size effect, the number of atoms in the system is increased to 10000. Another simulation study has been performed for the effects of six cooling rates on microstructure during solidification of liquid metal Zn. It is found that the glass transition temperature Tg decreases with the slower of cooling rate. It is still demonstrated that the effects of different cooling rates on the microstructures of metal Zn are very small in the liquid and supercooled states, but they are fully displayed below the liquid-solid transition points.