Microstructure and wear resistance of laser-cladded Ni-based composite coatings on downhole tools

Single- and graded-composite coatings of Ni35+tungsten carbide (WC), Ni35+original sialon powders (OSP), and Ni35+WC+OSP were prepared by laser cladding on 45 steel substrates, and their microstructures, hardness, and wear resistance were compared among different coatings. The high content of hard-phase WC, CrFe7C0.45, Cr4Ni15W, and AlNi3 could effectively improve the hardness and wear resistance. The hardness and wear resistance of the graded coatings were better than that of the single-composite coatings except the Ni35+WC+OSP composite coatings. The types of variation in the hardness of different coatings, such as the step increase and linear increase, were characterized by the distribution of hard phase. The maximum microhardness of the coatings reached 1118 HV0.5, which was approximately 5.8 times that of the substrate. The wear loss of the Ni35+WC graded coating showed much greater decrease, nearly double that of the substrate.