高温高压下Ag-Mg-Zn合金中金属间化合物的微观结构与热动力学性质的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法,研究了Ag-Mg-Zn合金中金属间化合物AgMg,Mg4Zn8和Ag8Mg4Zn4在高温高压下的结构稳定性、弹性性能和热动力学性质.理论计算结果与实验值和其他的理论结果符合得非常好.研究表明:金属间化合物AgMg,Mg4Zn8和Ag8Mg4Zn4在零温零压下是力学稳定的；Mg4Zn8和Ag8Mg4Zn4为延性相,而AgMg则为脆性相；在这三种金属间化合物中,Ag8Mg4Zn4的塑性最好,AgMg的塑性最差.利用准谐Debye模型,讨论了高温高压下Ag-Mg-Zn合金中金属间化合物的摩尔振动内能Uvib,m,摩尔Helmholtz振动自由能Avib,m,摩尔振动熵Svib,m,摩尔定容热容Cv,m,摩尔定压热容Cp,m,热膨胀系数α,Griüneisen 参量γ和Debye温度(O).

First-principles calculations of microstructure and thermodynamic properties of the intermetallic compound in Ag-Mg-Zn alloy under high pressure and high temperature

The structural stability, elastic and thermodynamic properties of the intermetallic compounds MgAg, Mg₄Zn₈ and Ag₈Mg₄Zn₄ in Ag-Mg-Zn alloy under high pressure and high temperature are investigated by employing the first-principles method based on the density functional theory. The theoretical results are generally in good agreement with experimental results and similar to the theoretical calculations. The calculated results indicate that the intermetallic compounds AgMg, Mg₄Zn₈ and Ag₈Mg₄Zn₄ are elastically stable at zero temperature and pressure. Mg₄Zn₈ and Ag₈Mg₄Zn₄ are of the ductility phase, and AgMg is of the brittleness phase. The plasticity of Ag₈Mg₄Zn₄ is the best in the three intermetallic compounds, and AgMg is the worst. Based on the quasi-harmonic Debye model the vibrational internal energy, vibrational Helmholtz free energy, vibrational entropy, heat capacity of constant volume, heat capacity at constant pressure, thermal expansion coefficient Grüneisen parameter and Debye temperature of the intermetallic compounds in Ag-Mg-Zn alloy under high pressure and high temperature are all discussed.