Comparison of electrochemical behavior of hydroxyapatite coated onto WE43 Mg alloy by electrophoretic and pulsed laser deposition

Surface modification of biodegradable magnesium implants to improve the surface-related properties and longevity is of crucial importance. This paper compares the corrosion behavior of hydroxyapatite (HAp) coated WE43 Mg alloy, developed using two different coating techniques viz. electrophoretic deposition (EPD) and pulsed laser deposition (PLD). The coated samples were tested for their corrosion behavior in Hank's balanced salt solution (HBSS) at 37 ± 2 °C. The higher adhesion of HAp obtained using PLD technique reduced the diffusion through coating and provided enhanced corrosion resistance to the bulk WE43 alloy. The corrosion rate was observed to be 0.073 mm/yr for HAp coated using PLD whereas, the coating developed by EPD and bare substrate had a corrosion rate of 0.194 and 0.97 mm/yr respectively. The electrochemical impedance spectroscopy (EIS) results obtained in the form of Nyquist and Bode plot further substantiated the results obtained using potentiodynamic polarization curve. The resistance offered by the solution was 51.5% lesser and the coating resistance was 96.87% higher for PLD coating than EPD coated sample. The SEM images of the HAp coated samples before and after corrosion clearly revealed that the degradation of HAp coated using EPD was higher compared to PLD. Hence, WE43 alloy coated with HAp by two different coating processes proves to have slower degradation rate in comparison with uncoated substrate and amongst the two coating processes PLD can be employed to develop successful coatings for application of Mg alloys in the field of orthopedics.