Effect of Hf additions on phase stability and mechanical properties of binary W-Hf alloys: A first-principles study

In this paper, the effect of hafnium alloying element on phase stability and mechanical properties of binary tungsten-hafnium alloys was calculated using the first principles technology. Firstly, we investigated the cell volumes, lattice constants and formation energies of binary W1-xHfx (x = 0, 0.0625, 0.125, 0.1875, 0.25 and 0.5) alloys. It is shown that binary tungsten-hafnium alloys remain maintain BCC structures. When the concentration of hafnium atoms is lower than 12.5%, the structures of binary tungsten-hafnium alloys are thermodynamically stable. The elastic constants of binary tungsten-hafnium alloys were calculated based on the optimized atomic lattice. Then the elastic modulus and other mechanical parameters are deduced according to the relevant formulas. It is shown that the mechanical strength of binary tungsten-hafnium alloy decreases with increasing hafnium concentration, which is lower than the mechanical strength of pure tungsten metal. However, the mechanical strength of binary tungsten-hafnium alloys is higher than that of pure hafnium metal. In addition, it can be effective to improve the ductility of pure tungsten metal based on hafnium alloying tungsten.