zA62镁合金中AB₂型金属间化合物的结构稳定性与弹性性能的第一原理计算

来源期刊：金属学报2010年第1期

论文作者：周惦武 徐少华 张福全 彭平 刘金水

文章页码：97 - 103

关键词：镁合金； 金属间化合物； 电子结构； 结构稳定性； 弹性性能

Key words：magnesium alloy； intermetallics； electronic structure； structural stability； elastic property

摘    要：采用基于密度泛函理论Castep和Dmol程序软件包,计算了ZA62镁合金中AB₂型金属间化合物MgZn₂,Mg₂Sn和MgCu₂的结构稳定性、弹性性能与电子结构。合金形成热和结合能的计算结果显示:Mg₂Sn具有最强的合金化形成能力,而MgCu₂结构最稳定;体模量(B)、弹性各向异性系数(A)、Young’s模量(E)、剪切模量(G)和Poisson比(v)的计算结果表明:MgZn₂和MgCu₂为延性相,而Mg₂Sn为脆性相,MgZn₂的塑性最好;采用弹性常数、体模量和结合能的经验公式计算金属间化合物的熔点,实验值均在采用弹性常数(±300 K)和体模量(±500 K)计算熔点预测的范围内,采用弹性常数比采用体模量和结合能预测熔点的平均相对误差小,其中采用弹性常数计算Mg₂Sn的熔点与对应的实验值十分接近,相对误差仅为0.31%。不同温度下热力学性质的计算结果表明,在298—573 K温度范围内,MgCu₂的Gibbs自由能始终最小,其结构热稳定性最好,结构稳定性的强弱顺序并不随温度的升高而消失;而对MgZn₂和Mg₂Sn,以475 K为临界,结构稳定性的强弱顺序随温度的升高发生了变化;态密度和Mulliken电子占据数的计算结果表明:MgCu₂结构最稳定的原因主要在于体系在Fermi能级以下区域成键电子存在强烈的离子键作用。

Abstract: Structural stabilities,elastic properties and electronic structures of Mg₂Sn,MgZn₂ and MgCu₂ in ZA62 magnesium alloy have been determined from first-principles calculations by using Castep and Dmol program based on the density functional theory.The calculated heats of formation and cohesive energies showed that Mg₂Sn has the strongest alloying ability and MgCu₂ the highest structural stability.The calculated bulk moduli(B),anisotropy values(A),Young’s moduli (E),shear moduli(G) and Poisson ratio(v) showed that MgZn₂ and MgCu₂ both are ductile,on the contrary,Mg₂Sn is brittle,and among the three phases MgZn₂ is a phase with the best plasticity.Their tested melting temperatures are within the ranges calculated from elastic constants(±300 K) and bulk moduli(±500 K),the estimated values from elastic constant have the smallest average relative error, the calculated melting temperature of Mg₂Sn phase is in well agreement with the experimental one and the error relative to the experiment result is about 0.31%.MgCu₂ has higher melting temperature,i.e. better structural stability among the three compounds.The calculations of thermodynamic properties show that the Gibbs free energy of MgCu₂ is also the smallest within 298-573 K range,indicating the structural stability of MgCu₂ does not change with the elevated temperature.The calculations of the density of states(DOS) and Mulliken electronic populations showed that the reason of MgCu₂ having highest structural stability in ZA62 magnesium alloy attributes to MgCu₂ phase having more ionic bonds below Fermi level compared with those of Mg₂Sn and MgZn₂ phases.