Effect of Al on structure and mechanical properties of Al x NbTiVZr ( x  = 0,0.5,1,1.5) high entropy alloys

The crystal structure, microstructure, microhardness and compression mechanical properties of Al_xNbTiVZr (x = 0, 0.5, 1, 1.5) high entropy alloy were examined. In the as solidified conditions, the alloys consisted from bcc matrix and C14 Laves phase. After homogenisation, the NbTiVZr alloy was bcc solid solution, whereas in Al containing alloys, C14 Laves phase and Zr₂Al particles were found in the bcc matrix. Volume fraction of second phase increased with Al concentration. Increase in Al content results in gradual decrease in density of the alloys from 6.49 g cm^− 3 of the NbTiVZr to 5.55 g cm^− 3 of the Al_1.5NbTiVZr alloy. The microhardness of the alloys was higher in the alloys with higher Al content and was generally proportional to the volume fraction of second phase particles. The compression yield strength of the alloys was of 960–1320 MPa, and NbTiVZr alloy was stronger than Al containing alloys. The ductility of the alloys gradually decreased with increase in Al content. The factors determining phase formation in the Al_xNbTiVZr alloys and effect of phase composition and chemical composition of individual phases on the mechanical properties are discussed.