Corrosion resistance enhancement of hydroxypatite and magnesium oxide multilayer coating on magnesium alloy az31 via electrophoretic deposition

Abstract

Magnesium (Mg) and its alloys have recently gained attention among researchers due to their excellent biodegradable and mechanical properties. However, poor corrosion resistance of Mg and its alloys have limited their clinical application. Rapid corrosion of Mg and its alloys may cause an implant failed before the bone has fully restored. The aim of this research was to enhance corrosion resistance of biodegradable implant substrate that is suitable for biomedical applications. Multilayer coating of nano-powders HA/MgO were coated on AZ31 magnesium alloy substrate via electrophoretic deposition (EPD) technique. A coating was obtained by applying suitable EPD process parameters (applied voltage and deposition time) and coating approaches (single layer coating and multilayer coating). The results of coating behaviour were characterised by means of XRD, and SEM to examine the coating surface morphologies and their phases. Coating performances of HA, MgO, and HA/MgO coating were studied by immersion test, potentiodynamic test, and electrochemical impedance spectroscopy where all done in-vitro. Elemental analysis was carried out using EDS to verify that the composed elements are biodegradable and harmless to the human body. The results obtained in this research suggested that corrosion resistance of a coated sample was affected by its particles distribution structure. Particles distribution structure with higher compactness showed a homogeneous coating layer and smaller surface defects. In general, the multilayer coating approach has outperformed the single coating approach by demonstrating a higher compactness particle distribution structure. Corrosion results of each group were compared, and the optimum process parameters were determined. The optimum process parameters for single layer coating HA, MgO and HA/MgO were 2min/10V, 30V/1min, and 15V/1min, respectively. On the other hand, the optimum number of layers for multilayer coating HA, MgO and HA/MgO were 5 layers, 3 layers, and 2 layers, respectively. It was also found that composite coating of HA/MgO has successfully inherited the benefits and limitations of each coating powder. Furthermore, defects such as agglomeration and cracks were found significantly reduced to a lower degree in multilayer coating approach. Among all of the coated samples, Laco-HA/MgO 2 layers coated with 5V/10 min each layer showed the highest corrosion resistance. The significant improvement in inhibition efficiency achieved 99.76% against the uncoated AZ31. Based on these results, it was concluded that this sample has a great potential for biodegradable orthopaedic application. Lastly, it was recommended to conduct cell viability measurement, biological reaction, and cytotoxicity test on Laco-2 layers by biological field researchers in the future.