Influence of pressure on the structural, elastic, hardness and thermodynamic behavior of Al-rich region TMAl12-type (TM=Mo, W and Cr) alloys

Abstract

Although transition metal (Mo, W and Cr) aluminides are regarded as the promising alloys, the high pressure behavior of the Al-rich region TMAl12 alloys is entirely unclear. Similar to MoAl12 and WAl12, the structure, mechanical and thermodynamic properties of CrAl12 are also unknown. To solve these problems, here, the structural stability, mechanical and thermodynamic properties of three TMAl12 alloys under pressure are studied by the first-principles calculations. The calculated results show that one novel cubic CrAl12 is firstly predicted. It is found that three TMAl12 alloys are thermodynamic stability under high pressure (<100 GPa). Importantly, the calculated bulk modulus of three TMAl12 alloys increases linearly with increasing pressure. In particular, the calculated bulk modulus under high pressure follows the order of WAl12>MoAl12>CrAl12. Naturally, the high bulk modulus of three TMAl12 alloys is that the pressure enhances the localized hybridization between TM atom and Al atom, which is confirmed by the bond strength of TM-Al bond. However, the shear modulus and Young's modulus of MoAl12 and WAl12 become smaller when the pressure is bigger than 70 GPa. The calculated hardness of three TMAl12 decreases with increasing pressure. I think that the high pressure maybe damaged the crystal structure of MoAl12 and WAl12. Importantly, the pressure results in the brittle-to-ductile transition of three TMAl12 alloys. In addition, the change of Debye temperature of three TMAl12 alloys is similar to the change of shear modulus and Young's modulus.