Effects of Y₂O₃ on microstructure and mechanical properties of AlCoCrFeNi high-entropy alloy coatings

AlCoCrFeNi high entropy alloy (HEA) coatings add by Y₂O₃ in the different mass fraction were prepared on Q235 steel matrix by laser cladding technology in this study, and the microstructure, hardness, and wear resistance of the AlCoCrFeNi high entropy alloy coatings were analyzed by X-ray diffractometer, scanning electron microscope, microhardness tester, and friction and wear tester. The results show that, the phase structure of AlCoCrFeNi HEAs coatings is composed of face-centered cubes (FCC) phase and body-centered cubes (BCC) phase. The volume fraction of BCC phase increases with the increase of Y₂O₃ mass fraction, while the FCC phase volume fraction shows the opposite trend. The microstructure of the AlCoCrFeNi high-entropy alloy coatings is composed of the equiaxed crystals, the addition of Y₂O₃ promotes the melt pool flow, makes the pores disappear gradually, improves the denseness, and makes the grains become fine. The addition of 5% Y₂O₃ (mass fraction) in the coatings results in the dendritic organization and the diffusely distributed YAl₂ and Y₂O₃ phases, and the coating microhardness reaches up to HV 350, which is about twice than that of the AlCoCrFeNi high-entropy alloy coatings, showing the obvious strengthening effect. The addition of Y₂O₃ is beneficial to promote the formation of BCC phase and the precipitation of YAl₂ phase in the coatings, which can effectively improve the hardness and wear resistance of the high entropy alloy coatings.