Microstructure evolution and tribological properties of laser cladding Stellite6-Cu/Graphene composite coatings on TC4 alloy

Abstract

There are still major limitations of their low hardness and insufficient wear resistance so far, although titanium alloys (TC4) are common materials used in key moving mechanical components. Hence, in this study, the Stellite6-Cu/Graphene coatings were prepared to employ laser cladding. The comprehensive characterization methods, such as XRD, SEM, XPS, and Raman spectrum analysis, were conducted to investigate the effect of adding graphene on the microstructure, microhardness, and tribological performances of samples. The main phase component of composite coating consisted of γ-Co solid solution, carbides (such as Cr₂₃C₆, Cr₇C_3, and TiC), and CuTi_x intermetallic compound, which were uniformly distributed into the interdendritic region and played a key role in realizing the grain refinement. This helped to greatly improve the strength and tribological performance of coatings. On a sliding tribo-pair system, the friction and wear properties of the substrate and coatings were studied, and the wear mechanisms of the samples were analyzed. The results indicate that in all composite coatings, the M2 composite coating with 1.2 wt% graphene achieved a twice increase in the microhardness compared with the raw substrate. The excellent lubrication effect of the graphene tribo-film resulted in significant reductions in friction (30 %) and wear (98 %) relative to the substrate under room temperature. At this temperature, slight adhesive wear and slight oxidative wear were the main worn mechanisms. Under a high temperature of 600 °C, the friction coefficient and wear rate were reduced by 55 % and 64 %, respectively, as compared to the substrate. This was mainly caused by the presence of oxidized tribo-film containing massive oxides and few graphene, with the mechanisms of slight abrasive wear and oxidative wear. This work is expected to provide certain data support for applying TC4 alloys in the wear-critical field.