Bond strength of plasma-sprayed hydroxyapatite/Ti composite coatings

One of the most important clinical applications of hydroxyapatite (HA) is as a coating on metal implants, especially plasma-sprayed HA coating applied on Ti alloy substrate. However, the poor bonding strength between HA and Ti alloy has been of concern to orthopedists. In this paper, an attempt has been made to enhance the bonding strength of HA coating by forming a composite coating with Ti. The bioactivity of the coating has also been studied. HA/Ti composite coatings were prepared via atmospheric plasma spraying on Ti-6Al-4V alloy substrates. The bond strength evaluation of HA/Ti composite coatings was performed according to ASTM C-633 test method. X-ray diffractometer and scanning electron microscopy were applied to identify the phases and the morphologies of the coatings. The bioactivity of HA/Ti composite coating was qualified by immersion of coating in simulated body fluid (SBF). The obtained results revealed that the addition of Ti to HA improved the bonding strength of coating significantly. In the SBF test, the coating surface was covered by carbonate-apatite, which was testified by X-ray photoelectron spectroscope, indicating good bioactivity for HA/Ti composite coating. The bioactivity of the coating has not been reduced by the addition of Ti.