Stability and fracture mechanism of α-Fe/V6C5 interface in high vanadium Fe-based alloys by first-principles calculations

Abstract

V6C5 is one kind of typical and stable vanadium carbides observed in the experiments. The α-Fe/V6C5 interface properties have an important effect on the mechanical properties of high vanadium Fe-based alloys, but the interface structure and fracture mechanism are unknown. Herein, the properties of α-Fe(001)/V6C5(001) coherent interface are studied by first-principles calculations including surface energy (σ), work of adhesion (Wad) and interfacial energy (γint). According to the results of work of adhesion and interfacial energy, MT stacking sequence of V-termination (V-MT) is the most stable interface structure. The electronic structures of α-Fe (001)/V6C5(001) interfaces reveal the formation of Fe-V, Fe-C and V-C bonds. A large amount of charge transfer between Fe and C (V) and shared electrons are in the interface, indicating that these bonds are a mixture of ionic and covalent bonds. However, during the first-principles tensile simulation, the V-terminated interface is finally destroyed due to the fracture of Fe-V bonds at the interface, while a new structure about Fe and C is formed at the C-terminated interface. The strong Fe-C bonds lead to the better tensile performance of C-terminated interface than V-terminated interface. This work provides a deeper understanding on the strengthening mechanism of high vanadium Fe-based alloys.