Microstructure and properties of composite coatings by laser cladding Inconel 625 and reinforced WC particles on non-magnetic steel

Due to the extremely complex and strict service conditions of non-magnetic drill collars, the friction, wear and corrosion will lead to their damage and failure. Therefore, the surface modification technology can be used to substantially improve the surface performance and effectively extend the service life of non-magnetic drill collars. Under this engineering background, the laser cladding technology was employed to fabricate pure Inconel 625 and Inconel 625/WC coatings on the surface of TWZ-2 non-magnetic steel substrate, and the influences of WC content on the microstructure, phase composition, element distribution, microhardness and wear and corrosion resistance of these coatings were analyzed. The experimental results show that the microstructures of pure Inconel 625 and Inconel 625/WC coatings are all composed of planar grain, cellular grain, columnar grain and equiaxed grain successively. The phases of pure Inconel 625 coating are composed of γ-Ni phase and Laves phase. With WC particles mixed into Inconel 625 powder, various carbide phases appear in the composite coatings. The higher the WC content, the more the precipitated carbides formed by the reaction, thus aggravating the segregation of the solid solution strengthening elements. Besides, W and C elements present severe local segregation due to the undissolved WC particles. In terms of the hardening and strengthening effects of WC particles, the microhardness of the coatings gradually increases with the rise of WC content. The wear mechanisms of substrate and coatings are all compound wears, and different wear forms have different priorities. Accordingly, the wear mechanisms would change with the WC content. The higher the WC content, the lower the wear loss of coating, and the better the wear and friction resistance. Moreover, the corrosion resistance of coatings is better than that of substrate. With the increase of WC content, the corrosion resistance of the composite coatings decreases gradually.