Microstructure, phase composition and wear resistance of low valence electron concentration Al x CoCrFeNiSi high-entropy alloys prepared by vacuum arc melting

The low valence electron concentration (VEC) Al x CoCrFeNiSi ( x = 0.5, 1.0, 1.5 and 2.0) high-entropy alloys (HEAs) were designed by the fundamental properties of the constituent elements and prepared by vacuum arc melting method. The effects of Al addition on the crystal structure and microstructure were investigated. The microhardness and wear property were also researched. The results showed that the microstructure transformed from dendritic crystal to equiaxed crystal. It was found that FCC phase gradually decreased with the increasing Al content and disappeared until in a composition of 1.0 in Al x CoCrFeNiSi HEAs. Little FCC phase was found with continuously adding Al, while the phase fraction of BCC increased from 85.0% to 91.8%, and VEC decreased from 7.00 to 6.14. The microhardness was increased gradually from 598 up to 909 HV with addition of Al from 0.5 to 2.0. It was the same of the compressive strength results, which improved from 1200 to 1920 MPa. The wear coefficient and mass loss were in line with mechanical properties evolution, which was attributed to the microstructure transformation into equiaxed crystal and the increase in BCC phase.