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

•The structural and mechanical properties of Hf–B system are studied by first-principles.•HfB2 with hexagonal structure is more stable than other Hf–B compounds.•The mechanical properties of HfB2 are better than other Hf–B compounds.•The bond orientation plays an important role in strength for Hf–B compounds.

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.

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