Investigation on microstructure and properties of laser cladded AlCoCrCuFeNi high entropy alloy coating by ultrasonic impact treatment

The application of high entropy alloy (HEA) as coating materials has become a research hotspot. The combination of laser cladding technology and ultrasonic impact treatment (UIT) may provide an opportunity for better performance of HEA and it is possible to enhance the application prospect of HEA. To research the effects of UIT on microstructure and properties of laser cladded HEA coating, AlCoCrCuFeNi HEA coating was prepared by means of laser cladding and UIT was applied to strengthen the surface properties of AlCoCrCuFeNi HEA coating. The phase structures of laser cladded AlCoCrCuFeNi HEA coating were composed of FCC and BCC phases. There were no new phases formed in the AlCoCrCuFeNi HEA coating after UIT, while the BCC phase volume fraction was increased. Additionally, a hardening layer with a depth of ~15 μm was formed at the top surface and the average values of grain sizes were refined from 34.4 μm to 18.6 μm. As expected, the hardness of AlCoCrCuFeNi HEA coating with UIT was significantly improved to 715 HV0.2 benefitted from the nano crystal structure and enhanced plastic deformation and then decreases gradually along the depth to approximately the same hardness value as that of without UIT (530 HV0.2). More impressively, the impact hardening AlCoCrCuFeNi HEA coating exhibited higher corrosion resistance in 3.5% NaCl solution resulting from the lower surface roughness and fewer microstructure defects.