First-principles investigation of the structural stability and mechanical properties of TM3Al2C(TM=Mo, Cr and W) carbides

Although Mo3Al2C MAX phase is a promising high temperature ceramics because of the high temperature strength and excellent oxidation resistance, the structural and mechanical properties of Mo3Al2C-type carbide is unknown. Here, we apply the first-principles method to study the structural stability, mechanical and thermodynamic properties of TM3Al2C MAX phase. Three refractory metals (TM=Mo, Cr and W) are considered. The calculated results show that the formation enthalpy follows the sequence of Mo3Al2C<Cr3Al2C<W3Al2C. Naturally, the structural stability of TM3Al2C carbides is determined by the formation of TM-Al bond, TM-C bond and TM-TM bond. Importantly, it is found that three TM3Al2C carbides are mechanical stability because the calculated elastic constants of these carbides meet the Born stability criteria. The calculated elastic constant C-11 of W3Al2C is 321.0 GPa, which is larger than the elastic constant C-11 for Mo3Al2C and Cr3Al2C. Importantly, the bulk modulus of W3Al2C is 249.9 GPa, which is larger than the elastic modulus of Mo3Al2C and Cr3Al2C. In addition, three TM3Al2C carbides show better ductility. Naturally, the bulk modulus of TM3Al2C is related to the TM-C bond and TM-TM bond in a a-b plane. However, the strength of shear modulus of TM3Al2C depends on the TM-C bond and TM-Al bond along the b- axis.