Mg熔体凝固过程中的分子动力学模拟  

Molecular Dynamics Simulation during Solidification of Magnesium Melt

作　　者：孙慧[1] 坚增运[1] 姜冰清[2] 刘翠霞[1] SUN Hui;JIAN Zengyun;JIANG Bingqing;LIU Cuixia(School of Materials and Chemical Engineering,Xi＇ an Technological University,Xi＇an 710021,China;Organization Department,Xi＇an Technological University,Xi＇ an 710021,China)

机构地区：[1]西安工业大学材料与化工学院,西安710021 [2]西安工业大学组织部,西安710021

出　　处：《西安工业大学学报》2018年第3期205-213,共9页Journal of Xi’an Technological University

基　　金：国家自然科学基金资助项目(51401156;51301125;51371133)

摘　　要：为了研究Mg熔体凝固过程中晶体团簇和扩散系数的变化规律,采用分子动力学模拟方法研究了冷却速度对Mg熔体最终构型的影响规律,通过分析Mg熔体的径向分布函数、H-A键对分析和最大晶体团簇中的原子数,确定出Mg熔体凝固后获得理想非晶的冷却速度,最后对不同初始温度和不同保温温度下Mg熔体的扩散系数进行了研究.模拟结果表明当冷速小于等于1.0×10^(11.0) K·s^(-1)时,Mg熔体凝固后形成晶态组织,具有fcc结构;当冷速大于等于1.0×10^(12.5) K·s^(-1)时,Mg熔体凝固后形成非晶态组织;当冷速在1.0×10^(11.0) K·s^(-1)到1.0×1012.5 K·s^(-1)之间时,Mg熔体凝固后形成晶态结构和非晶态结构组成的混合组织,由fcc和hcp结构层状镶嵌排列构成.在同一保温温度下,Mg熔体的扩散系数随着保温时间的延长而减小,随着保温温度的降低,熔体中原子的均方位移逐渐减小;随着初始温度的不断升高,Mg熔体开始降温时的均方位移增加较快,随着降温过程的进行,温度越低均方位移的变化幅度越小,扩散系数也随之减小,当时间足够长时,均方位移不再变化,此时,扩散系数不再随着初始温度的改变而改变.In order to study the change of crystal clusters and diffusion coefficient during the solidification of liquid metal Mg,a molecular dynamics simulation was carried out to investigate the effects of the cooling rate on the final configuration of magnesium after rapid solidification.The cooling rate for the formation of a magnesium amorphous phase was determined by analyzing its pair distribution function,H-A bond index and the largest crystal cluster,then the diffusion coefficients of Mg melt at different initial temperatures and different holding temperatures were studied.The simulation results show that the crystal structure of fcc structure is obtained after the magnesium melt has been solidified at a cooling rate that is less than or equal to 1.0×10^11.0 K·s^-1.When the cooling rate is greater than or equal to 1.0×10^12.5 K·s^-1,the magnesium melt solidifies to form an amorphous structure.It changes into the crystal structure composed of fcc and hcp when the cooling rate is between 1.0×10^11.0 K·s^-1 and 1.0×10^12.5 K·s^-1.At the same holding temperature,the diffusion coefficient of Mg melt decreases with the increase of the holding time.The lower the holding temperature,the smaller the mean square displacement of the atoms in the melt.As the initial temperature rises,the mean square displacement grows faster when Mg melt is starting to cool down.During the cooling process,the change of the mean square displacement becomes smaller at a lower temperature;so does the diffusion coefficient.However,when the time is long enough,the mean square displacement stops changing and the diffusion coefficient does not change with the initial temperature.

关 键 词：分子动力学模拟 晶体团簇 非晶 临界冷速 扩散系数 

分 类 号：O79[理学—晶体学]