Influence of B Concentration on the Structural Stability and Mechanical Properties of Nb–B Compounds

Synthesizing and designing novel hard material is still a huge challenge to industrial applications. In this paper, the influence of B concentration on the structural stability, elastic properties, hardness, and chemical bonding of Nb–B compounds has been investigated by using a first-principles approach. Two previously unreported crystal structures of Nb2B and Nb2B3 were predicted. In particular, the hard mechanism of TMBs has been explored in detail. The convex hull has indicated that the NbB with an orthorhombic structure is the most stable structure among those Nb–B compounds. The bulk modulus of Nb–B compounds is related to the B concentration. However, Nb2B3 shows the highest shear deformation resistance and the strongest elastic stiffness. The calculated theoretical hardness of Nb2B3 is 33.5 GPa and can be considered as a potential superhard material. The high hardness and elastic properties are attributed not only to the B concentration and orientation of bonds but also to the chemical bonding bet...