Corrosion Behavior of Reactive Sputtered Al2O3 and ZrO2 Thin Films on Mg Disk Immersed in Saline Solution

Abstract

Magnesium has attracted a lot of attention over the last few decades due to its light weight and potential use as biomaterial. However, the poor corrosion resistance of magnesium restricts its practical use for application where exposure to aggressive aqueous media is unavoidable. This paper describes the growth, characterization and corrosion analyses of Al2O3 and ZrO2 thin film coatings aimed at slowing down the fast degradation of Mg in saline solution. In this study, different thicknesses of Al2O3 and ZrO2 were deposited on pure magnesium (99.95%) disk using pulsed-DC reactive sputtering process. The microstructure and phase analyses were performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The corrosion protection behavior of the Al2O3 and ZrO2 coated magnesium samples immersed in 0.9 wt% NaCl solution were evaluated using electrochemical measurement techniques, such as open-circuit potential (OCP), potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS). The microstructural analyses showed that the Al2O3 thin film coatings have circular grains between 5 and 25 nm, while the ZrO2 coatings have bigger ellipsoidal grains. The results from the electrochemical corrosion analyses showed that the Al2O3 coated Mg disk had corrosion resistance of approximately 3 times that of ZrO2 coated Mg disk. It was also observed that increasing the thickness of the Al2O3 coating improved the corrosion resistance of the Mg disk. These results suggest that Al2O3 and ZrO2 coating can be used to effectively control the fast degradation of magnesium for medical implant applications.