W2AlC: A new layered MAX phase to adjust the balance between strength and ductility

To adjust the balance between the strength and ductility of high-temperature material, we apply the first-principles calculations to explore the structural feature, elastic modulus and brittle or ductile behavior of M2AlC (M = Mo, Cr and W) layered structure MAX phase. In addition, the thermodynamic properties of M2AlC carbides are also discussed. The calculated results show that two novel M2AlC carbides: Mo2AlC and W2AlC are predicted. For M2AlC carbide, the M - C bond in layered structure plays an important role in strength and ductility. In particular, the W2AlC exhibits better ductility in while has high elastic modulus. Naturally, the strength and ductility of W2AlC are related to the bond strength and bond orientation of W-C bond in (W-C)-Al-(W-C) layered structure. The weak bond strength of W-C bond in shear direction improves the slip and then improves the ductility of W2AlC carbide with high strength. In addition, the calculated Debye temperature follows the order of Cr2AlC > Mo2AlC approximate to W2AlC. Therefore, we believe that W2AlC carbide with (W-C)-Al-(W-C) layered structure can optimize the balance between the strength and ductility of this M2AlC MAX phase.