Corrosion and wear resistance improvements in NiCu alloys through flame-grown honeycomb carbon and CVD of graphene coatings

To improve the corrosion and wear resistance of NiCu alloys, a protective carbon coating and graphene layer is deposited on the surface of an NiCu sample using the flame growth method and chemical vapor deposition (CVD), respectively. The physicochemical properties, nanohardness, hydrophobicity, friction, and corrosion behaviors of the carbonaceous coating layer on the alloy are characterized. The carbon coat consists of many carbon nanowalls, forming a honeycomb-like structure at the interface with the alloy. The effects of the carbon coating on both the corrosion and wear resistance of the NiCu alloy and the corresponding mechanisms are investigated. For anti-corrosion of the coated Monel alloy, the optimum flame time is determined to be 10 min, and its corrosion current density is reduced by 80.8 %, which is much higher than that of the graphene coating (60.3 %). In addition, as compared with bare NiCu, the wear rate of the carbon-coated samples is reduced by 98.9 %, which is nearly the same as that of their graphene counterparts. Nanoindentation tests indicate that the hardness of the carbon-coated Monel alloy is much greater than that of its graphene counterparts due to the lower carbon-growth temperature.