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 ≈ 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.