Effect of Hf Concentration on the Microstructure and Room Temperature Mechanical Properties of Light-Weight TiVZrNbHf_x (x=0-1.0) Refractory High Entropy Alloys

This work explores the effect of the Hf concentration on the constituent phase, microstructure, and room temperature mechanical properties of TiVZrNbHfx (x = 0-1.0) light weight refractory high entropy alloys prepared by the arc melting technique. The results show that the TiVZrNbHfx alloys possess a single disordered bcc phase and dendritic structure, with densities ranging from 6.47 +/- 0.03 to 8.69 +/- 0.02 g/cm(3). Elemental scan mapping reveals a relatively homogeneous distribution of all elements, although local concentrations of elements can be observed in the microstructures. The addition of Hf enhances the Vickers hardness, ultimate strength, and the 0.2% proof stress, which could be attributed to solid-solution-like strengthening mechanism. The TiVZrNbHf alloy exhibits the highest values of Vickers hardness (449.0 +/- 11.3 HV1), ultimate strength (1682.7 MPa), and the 0.2% proof stress (1291.8 MPa). However, the fracture strain decreases with the increase in Hf composition, from 39.9% (for TiVZrNb) to 18.1% (for TiVZrNbHf).