Microstructure and mechanical properties of lightweight Al CrNbTiV(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 /cm ³ 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 _0.2 CrNbTiV 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·cm ³/g. And Al _0.5CrNbTiV and Al _0.8CrNbTiV shows typical brittle feature. Cr ₂ Nb-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 _x CrNbTiV 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.