Microstructure and Compressive Mechanical Properties of Hf Doped TiVZrTaHfx Refractory High Entropy Alloys

TiVZrTaHfx (x = 0, 0.1, 0.2, and 0.3, molar ratio) refractory high entropy alloys were prepared by vacuum arc melting. XRD, SEM and compression tests were employed to characterize the effects of minor Hf doping on microstructure and compressive mechanical properties of the TiVZrTa alloy. The results indicated that TiVZrTaHfx alloys gradually transform from a multiphase BCC structure to a single-phase BCC structure with increasing Hf content. Correspondingly, as-cast microstructure evolves from the coexistence of reticular morphology and dendrites into a relatively uniform dendritic structure, and elemental segregation was weakened. The compression results showed that the yield strength increases from 1139 MPa to 1253 MPa, while the compressive strain increases from 5.2% to 10.4%. In addition, the fracture mode changes from quasi-cleavage-dominated fracture to a brittle-ductile mixed fracture with more evident plastic tearing features. These results indicate that minor Hf addition can simultaneously improve the strength and compressive strain of the TiVZrTa alloy.