Investigation on microstructure and properties of AlxCoCrFeMnNi high entropy alloys by ultrasonic impact treatment

Abstract

In the present study, ultrasonic impact treatment was applied to promote the as-cast AlxCoCrFeMnNi (x = 0, 0.5, 1.0 and 1.5) high entropy alloys, and the microstructures, phase composition and surface properties were investigated. The increase in Al mole fraction from 0 to 0.5, 1.0 and 1.5 led to the different phase compositions from single FCC, duplex FCC + BCC to single BCC phase as well as the increased microhardness and reduced corrosion resistance. Ultrasonic impact treatment did not change the phase compositions of AlxCoCrFeMnNi alloys, while the successive network structures were broken and the short rod-like structures formed rather than long strip-like structures in the impacted hardening layer. The microhardness of AlxCoCrFeMnNi alloys (x = 0, 0.5 and 1.0) were improved by 92% (approximately 308.5 HV, 312.5 HV and 450.8 HV, respectively) after ultrasonic impact treatment due to the refine microstructures and precipitation strengthening mechanisms. Owing to the application of ultrasonic impact treatment the surface roughness of AlxCoCrFeMnNi alloys (Ra = 0.54–0.57 μm) decreased. Additionally, the impacted hardening AlxCoCrFeMnNi alloys exhibited higher corrosion resistance than the as-cast alloys resulted from the lower surface roughness.