Corrosion and Bioactivity Properties of Calcium-phosphate PEO Coating on AZ31 Mg Alloy Reinforced by Forsterite (Mg2SiO4) Nanoparticles

In this study, for the first time, the Forsterite (Mg2SiO4) nanoparticles (NPs) with the size of about 25 nm were added to the phosphate-based electrolyte, and the characteristics and properties of the obtained plasma electrolytic oxidation (PEO) coating on AZ31 Mg alloy was investigated. The results of the potentiodynamic polarization measurements revealed that after one week of exposure to simulated body fluid (SBF) solution, the coating with Mg2SiO4 NPs possessed 12.30 kΩ cm2 polarization resistance, which was more than two times greater than that of the coating without NPs. The thicker coating layer, lower wettability, and also presence of Mg2SiO4 NPs inside the pores were responsible for enhanced corrosion protection in the Mg2SiO4 NPs incorporated coating. After three weeks of immersion in SBF solution, the in-vitro bioactivity test results indicated the ability of the NPs-containing coating to form apatite (Ca/P ratio of 0.92) was weaker than the coating without NPs (Ca/P ratio of 1.17). This could be attributed to the lower wettability of the coating with NPs and supports that the addition of the nanoparticles is not beneficial to the bioactivity performance of the coating.