Effect of interstitial nitrogen on physical and mechanical properties of Al_0.5CoCrNi high-entropy alloys: a first-principles study

Abstract The N-doped high entropy alloys (HEAs) have recently garnered significant interest for their outstanding mechanical properties, making them valuable structural materials within the industry, aerospace, and biomedical science. In this work, the impact of interstitial N atom on various properties of Al 0.5 CoCrNi HEA is investigated through first-principle calculations. Specifically, the changes in lattice constant, formation energy, elastic modulus, density of states, Vickers hardness, Debye temperature, energy factor, and charge density caused by the presence of interstitial N atom are analyzed. The results show that the interstitial N atoms lead to a decrease of the sample stability due to an increasing formation energy of the N-doped HEA. As the interstitial N content increases, the elastic module decreases, and an apparent anisotropy appears in N-doped HEA. Moreover, Vickers hardness decreases, suggesting the change of the stiffness and deformation characteristics. Compared to the N-doped tetrahedrons, the N-doped octahedrons exhibit high ductility due to an increasing Poisson’s ratio, a decreasing G/B ratio, and an increasing Cauchy pressure. The significant decreasing Debye temperature and average sound velocity reduces the thermal stability. The change of the electronic structure suggests the possibility for customizing electronic and optical properties. Additionally, the low energy factors for screw and edge dislocations promote dislocation nucleation in N-doped HEA. Charge density analysis reveals strong bonding characteristics, potentially affecting the chemical stability and reactivity. This work provides a unique perspective on the N-doped mechanical mechanism, and offers important insights for the advancement of advanced N-doped HEA.