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

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 HfB2 is more stability than other Hf-B compounds at ground state. The calculated bulk modulus, shear modulus, Young's modulus and theoretical hardness of HfB2 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 HfB2 is 40.7 GPa and the HfB2 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. (C) 2015 Elsevier B.V. All rights reserved.