Lattice stability, mechanical and thermal properties of a new class of multicomponent (Fe, Mo, W)6C η carbides with different atomic site configurations

Abstract Transition metal carbides are candidates for high-temperature structural ceramics because of their high melting point, high hardness, and high strength. However, one challenge is overcoming their high intrinsic brittleness. In this study, we investigated a new class of (Fe, Mo, W)6C carbides, which have three Wyckoff positions for metallic atoms (16d, 32e, and 48f) and one Wyckoff position for carbon (16c). These different Wyckoff positions provide a great opportunity to optimize the mechanical properties by the partial replacement of atoms at each Wyckoff position to obtain high-entropy carbides. The current results show that the phonon spectra have no imaginary frequency when Fe occupies the 16d or 32e positions, but a soft mode is observed when Fe occupies 48f. (Fe, Mo, W)6C η carbides have a higher fracture toughness compared with those of M3C and MC carbides owing to their low carbon content (14.3 at.%). The mechanical anisotropy of (Fe, Mo, W)6C is weak, which is beneficial for increasing the damage tolerance. The thermal expansion coefficients of the (Fe, Mo, W)6C η carbides are predicted to be approximately (8.5–9.5) × 10−6 K−1 at 1400 K.