熔体初始温度对液态金属Ni凝固过程中微观结构演变影响的模拟研究

采用量子 Sutton-Chen多体势, 对熔体初始温度热历史条件对液态金属Ni快速凝固过程中微观结构演变的影响进行了分子动力学模拟研究. 采用双体分布函数g(r)曲线、键型指数法、原子团类型指数法和三维可视化等分析方法对凝固过程中微观结构的演变进行了分析. 结果表明: 熔体初始温度对凝固微结构有显著影响, 但在液态和过冷态时的影响并不明显, 只有在结晶转变温度T_c附近才开始充分显现出来. 体系在1×10¹² K/s的冷速下, 最终均形成以1421和1422键型或面心立方(12 0 0 0 12 0)与六角密集(12 0 0 0 6 6) 基本原子团为主的晶态结构. 末态时, 不同初始温度体系中的主要键型和团簇的数目有很大的变化范围, 且与熔体初始温度的高低呈非线性变化关系. 然而, 体系能量随初始温度呈线性变化关系, 初始温度越高, 末态能量越低, 其晶化程度越高. 通过三维可视化分析进一步发现, 在初始温度较高的体系中, 同类团簇结构的原子出现明显的分层聚集现象, 随着初始温度的下降, 这种分层现象将被弥散开去. 可视化分析将更有助于对凝固过程中微观结构演变进行更为深入的研究. 关键词： 液态金属Ni 熔体初始温度 微观结构 分子动力学模拟

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

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 T_c. 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 1×10¹² 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.
Keywords： liquid metal Ni initial melt temperature microstructure molecular dynamics simulation