Cr、Mo和W对FeAl金属间化合物电子结构和力学性能影响的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算了B2型FeAl金属间化合物的Fe8Al8和Fe8XAl7(X=Cr,Mo和W)超晶胞系统总能量、结合能、晶格常数、弹性常数、态密度和差分电荷密度,研究了合金元素对B2型FeAl金属间化合物晶体结构、电子结构和力学性能的影响。根据系统驰豫和几何优化确定了合金系统的稳定晶体结构;计算结果表明:随着加入元素原子半径的增大,合金的晶格常数相应增大,Fe8WAl7的晶格常数最大,Fe8CrAl7的晶格常数最小。Cr、Mo和W的加入均提升了FeAl的体模量、剪切模量和弹性模量以及改善了FeAl的脆性,其中Mo的加入对FeAl的脆性改善作用最大。根据电子结构和Cauchy压力参数计算结果的分析,FeAl金属间化合物为脆性相,主要原因是其电子结构中Fe的s、p、d态与Al的s、p态存在电子轨道杂化,呈明显的共价键特征。合金元素改善FeAl脆性的微观机理为:合金元素原子以d轨道电子为主参与了FeAl金属间化合物的电子杂化,增强了FeAl合金的结合能力;合金元素原子的加入使电荷转移量增加,增强了原子间离子键成分的作用,提高了FeAl合金的稳定性。

First-Principles Study on Effects of Cr, Mo and W on the Electronic Structure and Mechanical Properties of FeAl Intermetallic Compounds

A B2-FeAl model was established, and the total energy, cohesive energy, lattice constants, mechanical properties, density of states, and the electron density difference of the models of Fe8Al8 and Fe8XAl7 (X=Cr, Mo, W) were calculated by the first-principles based on density functional theory. The stable crystal structures of alloy systems were determined according to structural relaxation and geometry optimization. The calculation and analysis show that with the atomic radius of the alloying elements increasing, the lattice constant increases, in which the largest is Fe8WAl7, and the smallest is Fe8CrAl7. Brittleness of FeAl is improved by Cr, Mo and W infiltration, in which the effect of Mo is the best; the bulk moduli, rigidity moduli and Young's moduli of FeAl are increased by Cr, Mo and W infiltration. According to the analysis of electronic structure and the Cauchy pressure, FeAl intermetallic compounds are brittle phase, mainly due to the orbital hybridization of s, p, d-state electronic of Fe and s, p-state electronic of Al in their electronic structures, showing obvious characteristics of covalent bond. Micro-mechanism for improving ductility of FeAl is that d orbital electron of alloying elements is mainly involved in hybridization of FeAl; in addition, increasing of the system transferring charge enhances the role of the ionic bond. These improve stability of FeAl intermetallic compounds