Microstructure and Properties of CoCrFeNiTi High-Entropy Alloy Coating Fabricated by Laser Cladding

CoCrFeNiTi high-entropy alloy (HEA) coating with constituent elements of equal molar ratio was fabricated by laser cladding on 40CrNiMoA alloy steel. The microstructure, microhardness, wear resistance, and corrosion resistance of the coating have been investigated. The coating exhibits typical dendritic morphology, composing of solid solution phase with FCC structure, χ phase with cubic structure, and Co2Ti phase with HCP structure. The microhardness of the CoCrFeNiTi coating (about 700 HV0.3) is about four times higher than that of the CoCrFeNi. According to the estimated strength increment by the simple rule of mixture, the significant improvement of microhardness of the coating can be mainly attributed to second-phase strengthening rather than solution strengthening. The CoCrFeNiTi HEA coating with the wear rate of 0.84 × 10−7 mm3/(N m) has better wear resistance than the substrate and CoCrFeNi HEA. The wear mechanisms of the coating were abrasive wear and low-cycle fatigue wear in the dry sliding process, accompanied by oxidation wear. The CoCrFeNiTi coating with the corrosion rate of 1.41 × 10−2 mm/a exhibits poorer corrosion resistance than CoCrFeNi HEA, due to the formation of microanode and microcathode regions. Yet, the sensitivity to localized corrosion of the CoCrFeNiTi coating is reduced, due to the formation of a thicker passivation film.