Gradient graphene reinforced titanium matrix composite coatings on Ti-6Al-4V by electron beam surface melting: Microstructure, tribological and corrosion performance

To broaden the application scope of titanium (Ti) alloys, it is essential to develop efficient and reliable surface modification techniques to address their inherent poor wear resistance. Graphene is regarded as a promising modifier. Nevertheless, the exertion of its self-lubricating effect after modifying Ti alloy surfaces strongly depends on the adopted treatment methods. Titanium matrix composite (TMC) coatings were fabricated on Ti-6Al-4V (TC4) alloy via electron beam surface melting using pre-placed FLG/SiC powders. The microstructural evolution, tribological properties and electrochemical corrosion performance of the coating were analyzed. Results show that the coating prepared at 25 mA has good forming quality and a typical depth-gradient microstructure, with FLG enrichment in the surface layer and TiC-FLG-TiC sandwich structures gradually coarsening toward the substrate. Owing to this distinctive gradient microstructure, the coating exhibits approximately 30% higher surface hardness, nearly 50% lower specific wear rate, a lower and more stable friction coefficient during sliding, earlier-formed and thicker tribological layers compared with the TC4 substrate. Furthermore, the coating demonstrates superior corrosion resistance in 3.5 wt% NaCl solution.