Improving surface resistance to wear and corrosion of nickel‑aluminum bronze by laser-clad TaC/Co-based alloy composite coatings

Abstract

TaC/Stellite X-40 Co-based composite coatings were fabricated on nickel‑aluminum bronze (NAB) substrates by laser surface cladding (LSC), aiming at improving wear and corrosion resistances of NAB in marine environments. The morphology, microstructure, microhardness, wear and electrochemical corrosion behaviors of the surface treated composite coatings were studied. The results showed uniform distribution of carbide and intermetallic reinforcements such as TaC, Cr3C2 and Co3Ta in γ-Co matrix which lead to improvements of resistances to wear and electrochemical corrosion. Microstructural analyses of the LSC coating containing 20 wt% TaC showed the presence of fine reinforcements with isocellular crystals in the surface region and refined columnar crystal near the substrate area, as well as metallurgical bonding between the LSC coating and the NAB substrate. With the increase of TaC content in the cladding powders, the number of the granular reinforcements in the LSC coatings increased gradually, and the particles became larger. The maximum average microhardness of the composite coating of 20 wt% TaC was about 771.7 HV0.2, which is approximate 6.2 times higher than that of the NAB substrate (125.1 HV0.2). The minimum average coefficient of friction (COF) of the composite coatings was about 0.303 and its wear rate was about 0.4 times that of the NAB substrate. The self-corrosion potential (−0.182) of the composite coating with 20 wt% TaC was significantly higher than that of the substrate (−0.298), and the current density was lower, which implies that the corrosion resistance of the coating was significantly improved.