Phase stability and mechanical properties of hafnium borides: A first-principles study

Abstract The correlation between structural stability and mechanical properties of Hf–B compounds is systemically investigated by first-principle calculations. The convex hull indicates that the HfB 2 is more stability than other Hf–B compounds at ground state. The calculated bulk modulus, shear modulus, Young’s modulus and theoretical hardness of HfB 2 are bigger than other Hf–B compounds, which are consistent with the variation of Poisson’s ratio and B / G ratio. Moreover, the calculated Vickers hardness of HfB 2 is 40.7 GPa and the HfB 2 has strong stiffness deformation resistant along the a- direction compared with the c- direction. The structural stability and mechanical properties of Hf–B compounds are related not only to boron concentration in a system but also to the localized hybridization and bond characteristic. We conclude that the large elastic modulus and high hardness of Hf–B compounds are mainly attributed to the network B–B covalent bonds. In particular, the bond orientation plays an important role in mechanical properties.