液态金属Cu凝固过程中晶体形核与生长及纳米团簇结构的演变特性

Nucleation and growth of crystals and evolution properties of nano-clusters during solidification processes of liquid metal Cu

采用分子动力学方法和Quantum Sutton-Chen(Q-SC)多体势,对含有5万个液态金属铜(Cu)原子系统在凝固过程中的晶体成核与生长规律及纳米团簇微观结构转变特性进行了模拟跟踪研究.运用Honeycutt-Andersen(HA)键型指数法和新的原子团类型指数法(CTIM-2)分析了金属Cu原子的成键类型和原子团簇微观结构演变特性.结果发现:在以1.0×1013K/s速度冷却时,体系最终形成晶态与非晶态结构共存的混合结构,非晶转化温度约为673K,结晶起始温度为373K.在以4.0×1012K/s速度冷却时,结晶起始温度为673K,系统形成以1421和1422二种键型或由其构成的面心立方(fcc)(12000120)和六角密集(hcp)(1200066)基本原子团为主体的晶态结构,尤其是由1421键型构成的面心立方基本原子团在晶核生长和纳米团簇结构形成过程中占主导地位.形核和生长过程对凝固微观结构演变特性有重要的影响.

A tracing simulation study has been performed on the rule of nucleation and growth of crystals and transition properties of microstructrues of nano-clusters during solidification process for a system consisting of 50000 liquid metal Cu atoms using the molecular dynamics method and Quantum Sutton-Chen many body potential. The bond-type index method of Honeycutt-Andersen （HA）and a new cluster-type index method （CTIM-2）have been used to analyze the bond-type and evolution properties of cluster configuration for metal Cu atoms. It is found that when the cooling rate is 1.0×10^13 K/s, the mixed coexistence structures of crystal and amorphous are formed finally in the system, and the glass transition temperature is about 673 K, crystallization starting temperature is 373 K. At the cooling rate of 4.0×10^12 K/s, the crystallization starting temperature is 673 K. The crystal structures are mainly formed with the 1421 and 1422 bond-types or with the fcc （12 0 0 0 12 0） and hcp （12 0 0 0 6 6） basic clusters formed by these bond-types in the system. Espeically, the fcc （12 0 0 0 12 0） basic cluster consisting of 1421 bond-type occupies a dominant position in crystal-growth and the forming processes of nano-cluster structures. The processes of nucleation and growth have important effects on the evolution properties of solidification microstructures.