Influence of Ir concentration on the structure, elastic modulus and elastic anisotropy of Nb-Ir based compounds from first-principles calculations

Although Nb-Ir compounds are promising high-temperature structural materials due to the high melting-point, moderate density and excellent thermal stability, the structural stability and mechanical properties of Nb-Ir compounds are unclear. Here, we investigate the influence of Ir concentration on the structure, elastic modulus, elastic anisotropy and brittle-or-ductile behavior of Nb-Ir based compounds by using the first-principles calculations. Six Nb-Ir compounds are considered. The results show that the structural stability of Nb-Ir compounds strongly depends on the Ir concentration. In particular, NbIr3 is more thermodynamically stable than the other Nb-Ir compounds. The calculated elastic modulus of Nb-Ir compounds (except for Nb5Ir3) increases with increasing Ir concentration. The calculated bulk modulus, shear modulus and Young's modulus of NbIr3 are much larger than that of other Nb-Ir compounds. It is found that the high elastic modulus of NbIr3 is attributed to the strong and symmetrical Nb-Ir and Ir-Ir metallic bonds. Compared to other Nb-Ir compounds, Nb3Ir and NbIr3 have the smallest percentage anisotropy in compressibility. However, Nb3Ir2 has the highest percentage anisotropy in shear. Finally, our work indicates that NbIr3 is a promising high-temperature structural material, which is potential used in advanced aerospace and automotive applications. (C) 2019 Elsevier B.V. All rights reserved.