Simulation study of effect of initial melt temperature on microstructure evolution of liquid metal Ni during solidfication process

Abstract

A molecular dynamics simulation study is performed on the effect of the thermal history of initial melt temperature on the microstructure evolution in solidification process of liquid metal Ni by means of quantum Sutton-Chen n-body potential. The pair distribution function g(r) curves, the bond-type index method, the cluster-type index method and the three-dimensional (3D) visualization method are used to analyze the microstructure evolution in the solidification process. It is found that the initial melt temperature plays a critical role in the evolution of microstructures, but it is not obvious in liquid and supercooled states and the effects can be fully displayed only near the crystallization transition temperature Tc. The 1421 and 1422 bond-types or the FCC (12 0 0 0 12 0) and HCP (12 0 0 0 6 6) cluster in the system play the critical role in the microstructure evolution. The results show that at a cooling rate of 11012 K/s with different initial melt temperatures, the solidification structures of liquid metal Ni are always crystallized, but the numbers of the main bond-types and clusters have a vast varying range, and it does not vary linearly with the decrease of initial melt temperature. However, the system energy changes linearly with the decrease of initial melt temperature. Through the 3D visualization method, it is also found that atoms of the same cluster are gathered in the same layer when the system has a higher initial temperature, and these layers would be scattered when the initial melt temperature decreases. The 3D visualization method would help to deeply investigate the evolution mechanisms of microstructures in liquid metals during solidification.