Tuning the long-term corrosion behaviour of biodegradable WE43 magnesium alloy by PEO coating

Abstract

Plasma electrolytic oxidation (PEO) coatings can control fast degradation of next-generation biodegradable magnesium alloys for biomedical applications. In this work, we studied the effect of a PEO coating on the long-term corrosion behaviour of medical-grade WE43 magnesium alloy. In vitro experiments were performed for periods of up to 4 weeks in an organic fluid Dulbecco's Modified Eagles' Medium (DMEM). The average corrosion rates were measured using the hydrogen evolution method, and the degradation of the mechanical integrity were quantified by tensile test. Susceptibility towards localized corrosion was evaluated by scanning electron microscopy (SEM) images of cross-sections. Moreover, energy-dispersive X-ray spectroscopy (EDS) mappings and X-ray diffraction (XRD) were utilised for analysing the corrosion layer. Experimental results reveal significant changes in the product layer formation due to the PEO coating in phosphate-based electrolyte. The porous morphology of the coating with an initial thickness of ∼20 ± 5 μm changed significantly during the corrosion process, and a growing Mg-O-rich layer of 32 μm after 28 days was detected at the substrate interface. In contrast to the non-coated control group, no carbon-enriched area was observed. These findings imply significant long-term corrosion protection of the PEO coating. The results provide valuable information for a better understanding of the in vitro degradation process in PEO-coated magnesium alloys.