Microstructure Evolution and Tensile Properties of the Alx(CoCrNi)100-x Medium-Entropy Alloys

A series of Al-x(CoCrNi)(100-x) (x = 0-21 at.%) medium-entropy alloys (MEAs) were designed and prepared to investigate the effects of Al addition on the microstructures and tensile properties. The results reveal that the lattice structure changes from the initial single FCC structure (x < 10 at.%), to the FCC and disordered BCC structures (x = 10 and 11 at.%), then to the FCC and BCC/B2 structures (11 < x < 21 at.%), finally to the duplex BCC/B2 structures (x >= 21 at.%) with increasing Al addition. Consistent with microstructures, significant changes also occur in the corresponding tensile properties with Al addition, showing that the strength increases and the ductility decreases with increasing Al addition. Especially, the Al-15 MEA exhibits an acceptable balance of strength and ductility. Furthermore, the mechanism of microstructure evolution and the correlation between microstructures and tensile properties were also discussed and clarified.