Microstructures And Properties Of Laser Cladding High-entropy Alloy Coatings On SUS304

It has generally accepted that alloys are based on one principal element to serve as a matrix, with addition of various alloying elements to improve their properties. However, high-entropy alloys broke through the limitation of conventional alloys design and contained at least five elements with the concentration of each element ranging from 5 to 35 at.%. High-entropy alloys have attracted strong research interests and showed promising performance such as high hardness and excellent wear resistance.In this paper, high-entropy alloys coatings Al2 CrFeNiMox and AlCrFeNiMo0.5Nbx were synthesized by laser cladding on SUS 304. Phase composition and microstructure of the alloys were studied using X-ray diffraction (XRD), optical microscope (OM) and scanning electron microscopy (SEM). The chemical compositions of different regions were calculated from Energy Dispersive Spectroscopy (EDS). Mechanical properties were measured in the hardness testing and dry sliding wear testing.Results showed that high-entropy alloys coatings consisted of cladding zone (CZ), bonding zone (BZ) and heat affect zone (HAZ). Al2CrFeNiMox coatings were composed of two BCC solid solutions and the morphology of cladding zone was equiaxed grains. With more Mo content addition, the equiaxed grains became coarse. Besides, a eutectic structure was also observed in the interdendritic regions as Mo content reached to 1.5. With the increase of Mo content, the surface hardness of the coatings exhibited linear law. Al2CrFeNiMo2 got the highest hardness 678HV, which was about three times than that of the substrate (243HV). Compared with the substrate, the wear resistance of Al2CrFeNiMox had been improved greatly. The wear width and depth of the coatings showed a first declined and then increased trend with Mo content increasing. Especially for the Al2CrFeNiMoi alloy, the lowest wear width and the least mass loss (9.8mg) indicated its best wear resistance.AlCrFeNiMo0.5Nbx coatings consisted of BCC solid solution and Nb-rich Laves phase. When Nb content is between 0 and 1, the microstructure of high-entropy alloys was dendritic morphology. With Nb content increasing, the size of the primary phase BCC solid solution decreased while Laves phase grown. Besides, equiaxed grains were observed in the coating and the primary phase was Laves phase as Nb content reached to 1.5. The hardness of the coatings increased with increasing Nb content and AlCrFeNiMo0.5Nb1.5 got the highest hardness 684.8 HV. With the increase of Nb content, the wear scar width and depth decreased gradually, which was consistent with the change of wear mass loss. AlCrFeNiMo0.5Nb1.5 showed the best wear resistance because its wear mass loss 8.7mg was the lowest.