Study on microstructure and properties of laser cladding Cu/10Sn5Bi alternating stripe coating

Abstract

To address the limitations of traditional laser-cladded Cu10Sn5Bi self-lubricating coatings, a surface coating design featuring an alternating stripe structure is proposed in this study. A Cu/10Sn5Bi alternating stripe coating with a KF-Ni15 transition layer was applied to 45 steel. The macroscopic morphology, microstructure, phase composition, microhardness, tribological properties, and wear mechanism of the alternating stripe coating were investigated. The results indicate that a very thin “hard band” (approximately 17 μm) forms at the interface between the Cu layer and the 10Sn5Bi layer, primarily composed of the Cu3Sn intermetallic compound, along with a small amount of Bi and Ni elements. XRD pattern analysis reveals that the alternating coating is primarily composed of free Bi, Cu3Sn, and CrC phases. The unique macroscopic morphology and microstructure of the alternating coating result in a surface hardness distribution of alternating soft and hard regions, enhancing the wear resistance of the coating. Compared to the pure copper coating, the friction coefficient of the Cu/10Sn5Bi alternating coating decreased significantly, reaching 0.39 with an increase in the filling rate of 10Sn5Bi. This result is primarily attributed to the high fluidity of free Bi, which promotes the formation of a friction film on the surface, the self-lubricating effect of Cu and 10Sn5Bi, and the supporting and pinning effects of the “hard band” containing Cu3Sn compounds, Ni, Bi, and other elements. This fully demonstrates that the alternating stripe structure design of the surface coating enhances the synergistic effects of lubrication and hard coating. The multi-phase coupling effect of 10Sn5Bi, free Bi, and Cu3Sn, formed by laser cladding the Cu/10Sn5Bi alternating stripe structure, imparts unique properties to the coating and offers valuable insights for the design and development of laser-cladded self-lubricating coatings.