Preparation of hydroxyapatite functionally gradient coating on titanium substrate using a combination of electrophoretic deposition and reaction bonding process

The major difficulty in fabricating hydroxyapatite (HA) coating on titanium substrate using the electrophoretic deposition (EPD) process is the full densification and crack prevention of the coating under the restricted sintering temperature. In this work, a combination of electrophoretic deposition and reaction bonding process was developed for the fabrication of HA/alumina (Al2O3) composite coating and HA functionally gradient coating (FGC) on titanium substrates at a relatively low sintering temperature of 850 °C. The results showed that the reaction bonding process enhances the coating's densification. The HA FGC with a thickness of about 40 μm was crack-free and exhibited obvious gradient variation in chemical composition and microstructure. The HA FGC also exhibited much higher bonding strength than HA coating with the same thickness.