Design of lightweight Ti3Zr1.5NbV refractory high-entropy alloys with superior mechanical properties

Refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their excellent mechanical properties. However, most RHEAs have high density and exhibit poor ductility at room temperature, which greatly limits their applications. In this work, a series of lightweight Ti3Zr1.5NbVx (x = 0, 1 and 2, respectively) RHEAs with high strength and good ductility were designed and prepared using vacuum arc melting. The effects of V content on the microstructure, mechanical properties and deformation mechanism of the as-cast Ti3Zr1.5NbVx RHEAs were investigated in details. The results showed that all the Ti3Zr1.5NbVx RHEAs exhibit a single body-centered cubic (BCC) phase and their densities are less than 6 g/cm3. With the increase of V content, the grain size of the Ti3Zr1.5NbVx RHEAs decreases from 436.1 to 81.2 μm, and the hardness increases from 199.7 to 297.5 HV. The Ti3Zr1.5NbV2 RHEA possesses optimal tensile mechanical properties with the yield strength of 974.0 MPa, fracture elongation of 6.3%, and a specific yield strength of 165.7 MPa·cm3/g, better than most previously reported RHEAs. More importantly, the Ti3Zr1.5NbV2 RHEA also exhibits excellent elevated-temperature mechanical properties with yield strength of 770.9 MPa at 600°C and 243.6 MPa at 800°C. The deformation mechanism of the Ti3Zr1.5NbV2 RHEA is governed by dislocation slip, including planar slip bands, dislocation loops, and high density dislocation walls. The high strength of the Ti3Zr1.5NbV2 RHEA is mainly attributed to the solid solution strengthening effect, in which Zr and V elements play an important role.