Microstructure and mechanical properties of lightweight Al_xCrNbTiV(x = 0.2, 0.5, 0.8) refractory high entropy alloys

A novel lightweight refractory high entropy alloys Al_xCrNbTiV (x = 0.2, 0.5 and 0.8, in terms of molar ratios) are prepared by vacuum arc melting. In the as cast condition, the alloys have BCC phase with significant dendrite structure, with a low density of 5.82–6.38 g /cm³ and hardness increase from 462 HV_0.2 to 549 HV_0.2 with the solid solution strengthening effect by adding Al. Due to simultaneous dislocation motion and development of kink bands, Al_0.2CrNbTiV exhibits good combination of strength and ductility at room temperature, enabling deformation in compression to ε > 50%, with yield strength of 1570 MPa, and attractive specific yield strength of 246 MPa·cm³/g. And Al_0.5CrNbTiV and Al_0.8CrNbTiV shows typical brittle feature. Cr₂Nb-type C14 Laves phase precipitated with the compression temperature increase to 1000 °C. EBSD analysis shows discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) are activated together in the hot-compression process, and result in softening and a substantial increase in ductility of all the alloys. Furthermore, the theoretical yield stress of Al_xCrNbTiV is calculated through estimating the solid solution strength effect attributed to atomic misfit and modulus misfit, and the results indicated the degree of solid solution could affect the estimation accuracy.