Microstructural Evolution and Corrosion Behavior of ZnNi-Graphene Oxide Composite Coatings
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I.
INTRODUCTION
CORROSION protection of mild steel (MS) or other metal substrates by surface engineering has been extensively explored.[1–3] Zn-Ni coatings have attracted interest because of their excellent corrosion- and wearresistant properties.[4–6] These coatings are alternatives to conventional Zn coatings[7,8] and toxic cadmium coatings.[9,10] It has been illustrated that between the different compositions, ZnNi alloy coatings with 8 to 15 wt pct of Ni provide maximum corrosion protection to the underlying steel substrates.[11] Further enhancement in the corrosion resistance behavior of ZnNi coating has been achieved by the addition of foreign particles into ZnNi coatings.[12–17] Microstructure, mechanical and electrochemical properties of ZnNi-based composite coatings have been extensively explored. Hammami et al.[12] have reported on ZnNi-SiO2 nanoparticle composite coatings. They have shown that the addition of SiO2 particles facilitates formation of mixture of Zn and intermetallic phases in the coating microstructure, refines the grain size, increases the coating micro-hardness, and enhances the
M.Y. REKHA and CHANDAN SRIVASTAVA are with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India. Contact email: [email protected] Manuscript submitted 3 May, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
corrosion resistance performance of the coating. In another study, Praveen et al.[13] have investigated the corrosion behavior and hardness of ZnNi-TiO2 nanoparticle composite coatings. They have shown that incorporation of TiO2 nanoparticles enhances corrosion resistance and micro-hardness of the coatings. They have shown that the observed increase in corrosion resistance was primarily due to the removal of surface defects such as crevices, gaps, and micron holes because of the incorporation of TiO2 nanoparticles. In another study, Tuaweri et al.[14] have studied the corrosion resistance characteristics of ZnNi-SiO2 particle composite coatings. They have shown that the linear polarization resistance of the coatings increases with increase in the SiO2 particle content up to an optimum particle loading beyond which the polarization resistance decreases. They did not find any significant difference between the anodic dissolution current densities between pristine and composite coating. It was argued that the protection mechanism in case of ZnNi-SiO2 nanoparticle composite coating involved a combination of sacrificial and barrier protection of the underlying steel substrate. In another study, Exbrayat et al.[15] have investigated the morphology, composition, and corrosion behavior of pulse-electrodeposited ZnNi-ceria nanoparticle composite coatings. They have shown that the incorporation of ceria nanoparticles into the coating matrix is sensitive to the pulse parameter. It was shown that the incorporation of nanoparticles leads
to a significant enhancement in the corrosion resistance behavior of the coatings. In another study, Xiang et al.[16] have investigated the effect
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