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采用分子动力学方法对Mg7Zn3合金快速凝固过程进行计算机模拟,研究玻璃转变过程局域结构与动力学之间的关联。结果表明:以Mg原子为中心的FK多面体和以Zn原子为中心的二十面体局域结构,对Mg7Zn3金属玻璃的形成起关键性作用。Mg(Zn)原子的扩散系数在熔点附近开始偏离Arrhenius关系,而满足幂指数规律。根据均方位移、非相干中间散射函数和非Gauss函数等时间相关函数,发现:随着温度的降低,β驰豫越来越显著,α弛豫时间以VFT指数规律迅速增加;而且半径较小的Zn原子比Mg原子呈现较快的弛豫动力学行为。另外,部分短程有序局域原子结构具有较慢的动力学行为,对β驰豫中笼子效应起主导作用;并随着其数目的大量出现,体系扩散系数开始偏离Arrhenius关系,玻璃形成过程微观结构转变温度T Strg与动力学转变温度Tc非常接近。
The molecular dynamics method was used to simulate the rapid solidification process of Mg7Zn3 alloy to study the correlation between the local structure and kinetics of glass transition. The results show that the local structure of the FK polyhedron centered at Mg atom and the icosahedron centered at Zn atom play a key role in the formation of Mg7Zn3 metallic glass. The diffusion coefficient of Mg (Zn) atoms begins to deviate from the Arrhenius relation in the vicinity of the melting point, and satisfies the law of exponential. According to the time-dependent functions such as mean square displacement, incoherent intermediate scattering function and non-Gaussian function, it is found that β relaxation is more and more significant with the decrease of temperature, and the α relaxation time rapidly increases with the VFT exponent; Zn atoms exhibit faster relaxation kinetics than Mg atoms. In addition, part of the short-range orderly local atomic structure has a slow kinetic behavior, which plays a leading role in the β-relaxation cage effect. With the large number of occurrences, the diffusion coefficient of the system begins to deviate from the Arrhenius relationship and the microstructure of the glass The structure transition temperature T Strg is very close to the kinetic transition temperature Tc.