Analysis of corrosion behaviour and surface properties of plasma-sprayed composite coating of hydroxyapatite–tantalum on biodegradable Mg alloy ZK60

Magnesium (Mg) and its alloys are promising candidates for biodegradable bio-implants. However, the excessive corrosion in the physiological environment and subsequent decline in the mechanical integrity of Mg and its alloys have limited their utility as biomaterials. In the present study, an attempt has been made to improve the corrosion resistance of Mg alloy ZK60 plasma sprayed with tantalum (Ta)-reinforced hydroxyapatite coating. The experiment was conducted with three varied levels, i.e. 10, 20 and 30 weight percent (wt%) of Ta-content in hydroxyapatite coating. The coatings were characterized and in vitro corrosion behaviour was investigated by electrochemical measurements in Ringer's solution along with the analysis of surface properties. The corrosion resistance of the Mg alloy increased with the incremental increase in Ta reinforcement in hydroxyapatite coating. An increase in the protection efficiency was analysed for the Ta-reinforced hydroxyapatite coatings (∼10%, 18% and 23% for hydroxyapatite-10Ta, hydroxyapatite-20Ta and hydroxyapatite-30Ta, respectively) as compared to the pure hydroxyapatite coating. The hydroxyapatite coating effectively increased the surface hardness of the Mg alloy and Ta reinforcement further enhanced it. Surface roughness decreased with the incremental increase in Ta-content in hydroxyapatite coating. Wettability analysis revealed the hydrophilic nature of pure hydroxyapatite and Ta-reinforced hydroxyapatite coatings. The results of the study suggest that the proposed Ta reinforcement in hydroxyapatite is potentially important for biodegradable Mg bio-implants.