Mg17Al12、Al2Y及Al2Ca相稳定性与弹性性能第一原理研究

First-Principles Study of Structural Stabilities and Elastic Properties of Mg17Al12, Al2Y and Al2Ca Phases

摘要:

采用基于密度泛函理论的Castep和Dmol程序软件包，计算了Mg17Al12、Al2Y及Al2Ca相的结构稳定性、弹性性能与电子结构。形成热和结合能计算结果表明：Al2Y具有最强的合金化形成能力和结构稳定性；热力学性质计算结果表明：在298~573 K温度范围内，Al2Y的Gibbs自由能始终最小，其结构热稳定性最好，Al2Ca次之，Mg17Al12最差，Y和Ca合金化Mg-Al系合金形成Al2Y及Al2Ca利于提高镁合金的高温抗蠕变性能；弹性常数的计算结果表明：3种金属间化合物均为脆性相，Mg17Al12的塑性最好；采用弹性常数计算结果预测的Al2Y熔点最高，其结构热稳定性最好。态密度和Mulliken电子占据数的计算结果表明：Al2Y结构最稳定的原因，主要源于体系在Fermi能级以下区域成键电子存在强烈的共价键作用。

Abstract:

Structural stabilities, elastic properties and electronic structures of Mg17Al12, Al2Y and Al2Ca phases have been determined by Castep and Dmol program based on the density functional theory. The calculated heats of formation and cohesive energies show that Al2Y has the strongest alloying ability as well as the highest structural stability. The calculations of thermodynamic properties display that the Gibbs free energy of Al2Y is always the smallest and it has the highest stability within 298~573 K. The next is Al2Ca, and the last one is Mg17Al12. Y and Ca addition to the Mg-Al alloys can improve the heat resistance. The calculated elastic constants reveal that Mg17Al12, Al2Y and Al2Ca are all brittle, and among the three phases Mg17Al12 is a phase with the best plasticity. The results of elastic constant calculation predict that Al2Y has the highest melting temperature and the best structural stability. The calculations of the density of states (DOS) and Mulliken electronic populations indicate that the highest structural stability of Al2Y attributes to more covalent bonds below Fermi level compared with those of Mg17Al12 and Al2Ca phases.