Effect of in-situ synthesis of multilayer graphene on the microstructure and tribological performance of laser cladded Ni-based coatings

Abstract Graphene (Gr) has been regarded as the promising reinforcement for metal matrix composite coatings. However, it is hard to mix nano-scale Gr with micron-scale metal powders effectively at present, restricting the extensive application of Gr in engineering field. Therefore, this work proposed a new two-step method to in-situ synthesize multilayer Gr on the surface of Ni60 powders by combining ultrasonic and wet milling. Under protective atmosphere, Ni60 + Gr coatings were fabricated using laser cladding technique. In-situ synthesized multilayer Gr were successfully incorporated into Ni60 coatings, but part of them were transformed into the fullerene-like structures. In addition, a new matrix phase of Ni-Cr-Fe with bcc structure was generated in Ni60 + Gr coatings owing to the super adsorption effect of Gr on Ni, Cr and Fe atoms. The second phases such as chromium carbides in Ni60 + Gr coatings were refined and distributed more uniformly compared with that of Ni60 coatings. Furthermore, Ni60 + Gr coatings showed excellent tribological performance than that of Ni60 coatings, which was attributed to the synergistic effect between the lubrication of Gr or fullerene-like structures and the superior dispersion strengthening of the second phases.