Mg-Al-Ca合金系金属间化合物的力学性质与热力学性能第一原理计算

采用基于密度泛函理论Castep和Dmol程序软件包,计算了Mg-Al-Ca合金系金属间化合物的力学性质与热力学性能。结果显示:DI3型结构Al4Ca为延性相,C15型结构Al2Ca与C14型结构Mg2Ca为脆性相,C15型结构Al2Ca塑性最差;采用弹性常数计算结果预测的Al2Ca熔点与实验值很接近,误差仅为4.06%;而不同温度下热力学性能的计算结果表明,在298.15~425K温度范围内,Al2Ca的Gibbs自由能最小,对应其相结构的热稳定性最好;而Al4Ca次之,Mg2Ca最差;随着温度的升高,Mg2Ca的Gibbs自由能下降最快,对应结构的热稳定性增强也最快;在525K以上时,Mg2Ca的结构热稳定性最好,其次是Al2Ca,而Al4Ca最差。

Mechanical and Thermodynamic Properties of Intermetallic Compound in Mg-Al-Ca Alloy from First-Principles Calculation

The mechanical and thermodynamic properties of intermetallic compound in Mg-Al-Ca alloy have been investigated by Castep and Dmol program based on the density functional theory. The results show that DI3-Al4Ca is a ductility phase, on the contrary C15-Al2Ca and C14-Mg2Ca are of very good brittleness in Mg-Al-Ca alloy, and among the three phases, C15-Al2Ca is a phase with the worst plasticity. The melting point of intermetallic compound are estimated based on the calculated elastic constants; it is found that the estimated values of Al2Ca are in well agreement with the corresponding experimental values and the error relative to the experiment result is about 4.06%. By calculating the thermodynamic properties of intermetallic compound in Mg-Al-Ca alloy at different temperatures, it is found that Gibbs free energy of Al2Ca is the smallest as well as has the highest structural stability within the temperature range of 298.15-425 K, the next is Al4Ca, and the last one is Mg2Ca. In addition, with the elevated temperature, Gibbs free energy of Mg2Ca is decreased at the most rapid speed, meaning that its structural stability may be improved more rapidly as well. When the temperature is above 525 K, the case is changed; it is found that Mg2Ca has the highest structural stability, the next is Al2Ca, and the last one is Al4Ca.