Microstructural Evolution and Corrosion Behavior of ZnNi-Graphene Oxide Composite Coatings

Abstract

This work correlates microstructural evolution and corrosion behavior of electrodeposited ZnNi-graphene oxide composite coatings. Incorporation of GO improved the coating compactness and decreased the surface roughness. Structural characterization revealed that the pure ZnNi coating contained only intermetallic phases (γ-NiZn3, γ-Ni3Zn22, and γ-Ni5Zn21), whereas ZnNi-GO coatings contained Zn phase along with the intermetallics. Addition of GO gradually increased the volume fraction of the Zn phase and reduced its crystallite size. With the addition of GO, a noticeable and systematic variation in the growth texture of the coatings was also observed. Corrosion resistance of the composite coating increased with increase in the addition of GO. Microstructural characterization revealed that the composite coating contained Zn phase along with the GO forming a Zn-GO matrix containing intermetallics. Further investigation of the GO extracted from the electrolyte bath revealed that during the electrodeposition process, Zn nucleated and grew over the GO in the electrolyte itself which led to the co-existence of Zn and GO in the coating matrix. Enhancement in the coating compactness, increase in the Zn phase which is sacrificial, and the impermeability of the GO led to the high corrosion resistance of the ZnNi-GO composite coatings when compared to the pure ZnNi coating.