非晶合金结构演变影响玻璃形成能力的分子动力学研究

The influence of structure evolution of metallic glass on glass forming ability by molecular dynamics study

通过分子动力学方法模拟了Ti_(75)Al_(25)、Ni_(50)Zr_(50)和Cu_(50)Zr_(50)非晶合金的玻璃转变过程,得到并分析了平均原子体积和双体分布函数等结构参数,并应用Voronoi多面体指数分析法统计了玻璃转变过程中二十面体及类二十面体团簇的数量,通过分析团簇在玻璃转变过程中种类和数量的涨落趋势,研究了非晶原子由短程序连接至中程序再至长程无序的动力学演化过程.结果表明,非晶合金的玻璃形成能力以及塑性变形能力与动力学演化过程中Voronoi团簇的种类和数量密切相关.在玻璃转变过程中局部五次对称性高的团簇倾向于连接在一起形成链,从而密排整个空间,降低系统的动力学行为从而提高玻璃形成能力.塑性形变倾向于发生在局部五次对称性较低的区域.在玻璃转变温度附近团簇种类和数量的突变反映出非晶合金的自组织临界行为,蕴含着丰富的非线性动力学现象.

The glass transformation processes of Ti_(75)Al_(25), Ni_(50)Zr_(50) and Cu_(50)Zr_(50) were simulated by molecular dynamics method. The average atomic volume and radial pair distribution function were obtained. Besides, the number of icosahedral and icosahedral-like clusters were calculated by Voronoi polyhedron index analysis. Eventually, the dynamic evolution of amorphous atoms from short order to medium order and then to long range disorder was studied by analyzing the type and number of clusters during glass transformation. The results show that the glass forming ability is closely related to the type and number of Voronoi clusters. Besides, the clusters with high local quintuple symmetry tend to join together in order to form chains during the glass transformation process, which densely fills the whole space and reduces the dynamic behavior of the system. Furthermore, the plastic deformation tends to occur at the area with low local quintuple symmetry. It is intriguing to note that the abrupt changes of the types and number of clusters near the glass transformation temperature reflect the self-organized criticality behavior of metallic glass.