两种金属的势能曲面特征及与玻璃形成能力的关系

Relationships between potential energy landscape and glass forming ability for two metallics

运用分子动力学模拟方法,采用镶嵌原子势,研究了金属Cu和Ni3Al在发生玻璃转变过程中的势能曲面.我们计算了两种金属的内在结构(Inherent Structure简称IS),发现它们的内在势能在整个降温区间分为三个阶段:高温时,内在势能在一个较高的能量值附近波动;当系统的温度降低到熔点温度(Tm)时,内在势能大幅度减小;当体系温度降到玻璃转变温度(Tg)时,内在势能变得平稳.本文将Cu,Ni3Al和Lennard-Jones Binary Mixtures(BMLJ)液体的内在势能进行了比较,发现金属势能曲面与BMLJ液体的势能曲面存在明显的差异,与BMLJ液体相比,Cu和Ni3Al在高低温的内在势能差值很小,尤其是Cu的内在能量几乎不随温度变化,其差值的大小反映了液体的动力学性质的强弱.文章统计了Cu和Ni3Al在不同温度下内在能量的概率分布,并计算了两种金属内在结构的海森矩阵特征值的概率分布,发现Ni3Al的势能曲面比Cu的势能曲面更粗糙,更易形成非晶.我们提出了一个由势能曲面计算流变激活能的新方法,并计算了Cu和Ni3Al的流变激活能,发现它们的激活能都随着温度的降低而升高,但是Ni3Al的激活能随温度降低升高得更快,在玻璃转变点附近,Ni3Al的激活能比Cu的激活能要高,这与Ni3Al比Cu有更好的玻璃形成能力有着密切的联系.金属的势能曲面的特征决定了金属的玻璃形成能力.

Potential energy landscapes(IS) of pure Cu and Ni 3 Al alloy during glass transition have been studied by a series of molecular dynamics(MD) simulations with embedded atom method(EAM) potentials.It is found that the inherent-structure energies reach a constant value independent of temperature at high temperature following by an abrupt decrease at intermediate temperature T m and a lower value again below T g.The temperature-dependent average energies of the inherent structures of liquid Cu and Ni 3 Al alloy are compared with that of Lennard-Jones Binary Mixtures(BMLJ) liquid,we note that the difference of inherent-structure energies between high and low temperatures which corresponding to the dynamics of liquid is significant for BMLJ liquid,whereas those of the liquid Cu and Ni 3 Al alloy are slight.The probability distribution of inherent-structure energies and Hessian eigenvalue with different temperature for liquid Cu and Ni 3 Al alloy were also calculated,and we found that the PES of Ni 3 Al is more rough which is easy for glass forming.The viscous flow activation energy which is calculated based on PES increases as the temperature drops,distinctly for Ni 3 Al alloy.Comparing with Cu,the activation energy of Ni 3 Al alloy is higher around the glass transition temperature which lead to better glass forming ability for Ni 3 Al.Glass forming ability in metallic liquid is obviously determined by its PES.