Theoretical calculation of elastic properties and electronic structure of B2 iron aluminides and ternary iron-aluminum alloys

The mechanical properties of FeAl and ternary Fe-X-Al (X = Cr, Mo) alloys are investigated using first-principles density functional theory (DFT), with the valence electron structures also being determined using the empirical electron theory of solids and molecules. The structural attributes of FeAl are fitted using an E-V curve, and the stable structures of the ternary alloys are systematically predicted along with their respective elastic constants and phonon frequencies. The bonding nature in FeAl is partly defined by covalence with orbital hybridization, which explains its intrinsic brittleness. The micro-mechanism by which the ductility of FeAl is improved by Cr or Mo addition is as follows: Cr or Mo addition increases the cohesive capacity of the bonds in FeAl; s, p, and d orbital electrons of the alloying element are mainly involved in the hybridization of FeAl; and the alloying elements increase the electron density of Fe and Al atomic bonding.