ABSTRACT

In this study, electrodeposited chromium (Cr) coatings are deposited on 304L stainless steel (SS) from a trivalent Cr bath at temperatures of 30°C and 80°C. For better adhesion of coating layer, a new pretreatment method was developed. The scanning electron microscope (SEM), 3D profilometry and x-ray diffraction (XRD) results show that the coatings produced at bath temperatures of 30°C and 80°C are clearly distinct in thickness, composition, surface morphology and surface topography. The coating formed at 30°C has a higher carbide content, coating thickness and roughness, as well as a high degree of coating defect like cracks and pores, as compared to the crack-free coating electrodeposited at 80°C. From the XRD results, it is observed that amorphization of the Cr coating increases with decrease temperature. Finally, the electrochemical behavior of the coatings and the bare SS in 3.5 wt% NaCI environment were investigated with potentiodynamic polarization test. The results show that the localized (pitting) corrosion resistance of the 304L SS canister material is improved by the Cr coatings electrodeposited at 30°C and 80°C. Subsequently, pit quantification and characterization show that the coating produced at higher bath temperature has a better ability to suppress pitting and possibly chloride induced stress corrosion cracking (CISCC) than that produced at atmospheric temperature.

INTRODUCTION

Overtime, chromium has traditionally been used as surface coating in numerous industrial application such as automotive and general engineering products because of its excellent wear resistance, low coefficient of friction, high resistance to heat and corrosion.1 Owing to its advantages, several deposition methods have been developed to coat Cr on different surfaces such as plasma nitriding, vapor deposition, physical coating spray, electrodeposition and others.2-4 Among these techniques, electrodeposition stands out because of its simple and versatile approach of producing Cr deposit under ambient temperature and normal pressure, with benefits of low cost, high deposition rate, good homogeneity of coating thickness, and intriguing ability to coat substrates of complicated geometrical forms.2

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