Phase stability and mechanical properties of tungsten borides from first principles calculations

The phase stability and mechanical properties of tungsten borides W2B, WB, WB2, W2B5 and WB4 were extensively studied by first-principles calculations within density functional theory. The thermodynamic and mechanical stabilities were examined. Our calculations on the enthalpy–pressure relationship and convex hulls have demonstrated that at zero pressure, the experimentally observed W2B–W2B (W2B–W2B represents W2B in W2B structure type, the same hereinafter) and WB–WB, and assumed WB2–ReB2 phases are stable against decomposition into other components. The estimated hardness of WB2–ReB2 is 39.4 GPa, suggesting that it is a potentially hard compound. At 60 GPa, the most stable phases are WB–WB and WB2–WB2. WB–WB, WB2–AlB2 and WB4 are the ground state phases at 100 GPa. The phase transition mechanism for WB2 was discussed. The synthesis of WB2–AlB2 could be conducted at high pressures.