Quasi-in vivo corrosion behavior of AZ31B Mg alloy with hybrid MWCNTs-PEO/PCL based coatings

This study investigated the effects of multi-walled carbon nanotubes (MWCNTs) and polycaprolactone (PCL) on the quasi-in vivo corrosion behavior of AZ31B Mg alloy treated by plasma electrolytic oxidation (PEO). Thin (∼2 µm, PCTPCL4) and thick (∼60 µm, PCTPCL6) PCL layers were applied only onto the MWCNTs-PEO coating (PCT) as it showed better corrosion performance. Findings reveal that incorporation of MWCNTs induced several structural and functional modifications in the PEO coating, such as increased roughness, a thicker inner barrier layer, and reduced hydrophilicity. Quasi-in vivo corrosion testing was carried out under controlled temperature, pH, and fluid flow in simulated body fluid (SBF) by electrochemical impedance spectroscopy (EIS) and hydrogen evolution experiments. EIS results revealed that, after 48 h immersion, a diffusion process controlled hydration of the ceramic coatings. Comparison of the collected hydrogen after 15 days of immersion in the quasi-in vivo environment revealed that the PEO and PCT ceramic coatings decreased hydrogen generation by up to 74% and 91%, respectively, compared to non-coated alloy. PCTPCL6 coating exhibited the lowest amount of collected hydrogen (0.2 mL/cm2). The thick PCL layer delayed the onset of substrate corrosion for at least 120 h, reducing the corrosion rate by 85% compared with the PCT.