The influence of N content on structures and mechanical properties of FCC_(AlCrMoTiV)1-XNX high-entropy nitrides: A density functional theory (DFT) study based on site preference

Abstract

High-entropy nitrides (HENs) have been extensively studied for their exceptional mechanical properties, making them promising candidates for surface modification in machining tools and aerospace materials. However, the mechanisms by which nitrogen content influences the structure and mechanical properties of HENs remain unclear. This study constructed a theoretical model for ordered FCC_(AlCrMoTiV)_1-XN_X HENs based on the site occupying fractions (SOFs) of metal atoms and the preferred occupying distribution (POD) of nitrogen atoms. Using density functional theory, we investigated the microscopic structure and mechanical properties of these nitrides. The results show that the nitrogen content significantly affects the lattice distortion of HENs and the strength of chemical bonding, thereby altering their mechanical properties. At the ground state, the lattice distortion reaches a minimal value when the nitrogen content is 46.67 %, and the Youngʼs modulus $E$, and hardness $H$ are 361.06, and 22.58 GPa, respectively. In addition, we further predicted the temperature-dependent lattice distortion and mechanical properties of FCC_(AlCrMoTiV)_1-XN_X HENs. When nitriding reaches saturation, lattice distortion is most strongly influenced by temperature. The HEN with 41.82 % nitrogen content exhibits the most outstanding mechanical properties. Even when the temperature rises to 1273 K, it maintains a hardness of 17.38 GPa and retains its ductility.