Multi-layer graphene coating for corrosion resistance of Monel 400 alloy in chloride environment

Graphene coatings on Cu and Ni have been shown in the literature to remarkably improve corrosion resistance of these metals. However, the corrosion resistance of Ni-Cu alloy system (especially commercial alloys) due to graphene coating has remained unexplored. On the basis of the mechanistic understanding of corrosion resistance of graphene coated Cu and Ni, this study investigates development of an ultra-thin graphene coating over a Ni-Cu alloy (Monel-400 alloy) by chemical vapour deposition (CVD), and demonstrates a durable corrosion resistance offered by the coating. Raman spectroscopy confirmed the multilayer nature of the synthesized graphene coating. Electrochemical characterization showed the graphene coating to improve corrosion resistance of Monel 400 alloy by nearly two orders of magnitude in 0.1 M sodium chloride (NaCl) solution. The improvement in corrosion resistance is attributed to the ability of Monel 400 alloy to develop multilayer graphene that effectively masks the defects and provides complete coverage. Scanning electron microscopy corroborated with the electrochemical data has confirmed the presence of the graphene coating even after 1008 h of immersion in 0.1 M NaCl solution. Thus, the findings of this study suggest a promising approach to a durable corrosion resistance of Monel 400 alloy by CVD graphene coating for the first time.