Effect of hydrothermal treatment on microstructural feature and bonding strength of plasma-sprayed hydroxyapatite on Ti-6Al-4V

The effects of hydrothermal treating temperature on bonding strength pertaining to the microstructural evolution of plasma-sprayed hydroxyapatite coatings (HACs) on Ti-6Al-4V substrate were investigated. On the basis of the observed microstructure, the as-sprayed amorphous and impurity phases, such as α-Ca₃(PO₄)₂, Ca₄P ₂O₉ and CaO transform into crystalline HA after performing the hydrothermal treatment. Additionally, ultrafine crystallized particles can be recognized that the nucleation and grain growth occur by hydrothermal treatment at elevated temperatures of 175°C and 200°C. Furthermore, the hydrothermal treatment between 100°C and 150°C shows a significant decrease in microcracks, corresponding to an increase in bonding strength. This study reveals that even a small variation of hydrothermal heating temperature under 200°C can cause significant changes of the microstructural morphologies. Combining the experimental results of spraying defects, microstructural evolution and bonding strength, the knowledge of the hydrothermal-treated HACs will be helpful for the understanding and prediction in the biological stability and mechanical stability of HACs in the long-term clinical use.