The structural, magnetic, electronic, and mechanical properties of orthogonal/hexagonal M7C3 (M = Fe and Cr) carbides from first-principles calculations

Abstract

First-principles calculations were performed to investigate the structural, magnetic, electronic, and mechanical properties of orthogonal (o-)/hexagonal (h-) M7C3 (M = Fe and Cr) carbides. The o/h-M7C3 structural framework is formed by a 9-vertex Bernal polyhedron (triplet with C-prisms) combined with tetrahedra and octahedra attached to its free triangular faces. The total magnetic properties of the M7C3 carbide arise from the Wyckoff sites of Fe and Cr atom and Fe - (Fe, Cr or C) bond length. M7C3 carbides have the characteristics of covalent, metallic and ionic bonds. Cr substitution causes the reinforcement of the covalent bond of Fe–Cr. Fe3Cr4C3 has superior mechanical properties with higher hardness and strength, which indicates the probability of the excellent wear resistance of high chromium cast iron. This investigation provides a theoretical basis for obtaining the excellent physical properties of Fe-based materials.