Effect of alloying elements on mechanical, electronic and magnetic properties of Fe2B by first-principles investigations

First-principles calculations using density functional theory (DFT) were performed to explore the effect of common 3d elements M (M = Ti, V, Cr, Mn, Co, Ni and Cu) on the mechanical, electronic and magnetic properties of Fe2B. A formula of (Fe0.875,M0.125)2B was used. Firstly, the negative cohesive energy and formation enthalpy suggest that all the compounds are thermodynamically stable. With the knowledge of calculated elastic constants, the moduli, the Pugh’s modulus ratio G/B, the Poisson’s ratio v and the hardness of Fe2B and (Fe0.875,M0.125)2B were further predicted. Overall, with increasing atomic number, the moduli and hardness of the borides initially increase and then decrease. (Fe0.875,Cr0.125)2B possesses the largest bulk, shear and Young’s modulus simultaneously, while (Fe0.875,Mn0.125)2B has the largest hardness. The G/B and v values indicate that all the alloying elements are able to enhance the ductility of the Fe2B except Mn, but they do not change the nature of intrinsic brittleness of the Fe2B. Combined with the electronic structures, we revealed that the mechanical properties of the borides are mostly determined by FeB and MB bonds. FeFe bonds in 〈2 2 0〉 and 〈1 1 3〉 orientations are both covalent bonding. It can also be predicted that all the alloying elements reduce the magnetic moments (Ms) of the Fe2B mainly because the Ms of the substituted M atom is smaller than that of Fe atom.