Exploring the relationship between sputter-deposition conditions and electrochemical response of ZrO2 films on biodegradable MgZnCa alloy

Abstract

In this work, we investigated the enhancement of corrosion resistance in a biodegradable Mg-0.7Zn-0.6Ca (wt. %) alloy (MgZnCa) by applying ZrO2 thin films deposited via reactive magnetron sputtering. We employed a fractional factorial experimental design to systematically examine the influence of the deposition power, deposition time, and O2 fraction on the effectiveness of the ZrO2 thin film in preventing corrosion of the Mg alloy. Our analysis revealed that the ZrO2 thin films exhibited a monoclinic crystal phase and maintained stoichiometry across various O2 fractions. Interestingly, we observed a 78% roughness reduction when using the lowest O2 fraction, while roughness increased with the deposition power and time. The corrosion response of bare and ZrO2-coated MgZnCa alloy was assessed by electrochemical techniques and detection of H2 production during the Mg corrosion via gas chromatography. The optimal set of deposition conditions, essential for enhancing the short-term corrosion resistance of magnetron-sputtered ZrO2 coatings, involves maximizing thickness through high power (400 W) and extended deposition time (90 min). It is crucial to balance these factors while maintaining an appropriate O2 fraction (20%) to ensure the formation of a stoichiometric film. Avoiding excess oxygen is imperative, as it can lead to undesirable intergranular porosity and surface roughness. This optimization resulted in a 46% reduction in the evolution of H2 gas compared to the bare MgZnCa alloy. Overall, this work sheds light on the potential of ZrO2 thin films as effective corrosion-resistant coatings for MgZnCa alloys, emphasizing the critical role of deposition parameters in achieving superior protection against corrosion.