Effect of Apatite Precipitation on Failure Behavior of Hydroxyapatite Coating Layer on Titanium Substrate

Abstract

High reliable hydroxyapatite (HAp) coating on commercially pure titanium (cp-Ti) substrate with and without mixed hydroxyapatite/Titanium (HAp/Ti) bond coat was successfully developed by using plasma spraying. The four-point bending with Acoustic Emission attachment (AE) for evaluating failure behavior of the two kinds coated specimens was conducted to investigate the effect of bond coat layer on failure of the coating. The effect of apatite precipitation by immersing in conventional simulated body fluid (c-SBF) on failure behavior of the coated specimens were also investigated. The AE patterns obtained during four-point bending test of the specimens with apatite precipitation after immersion in c-SBF was compared with those of the specimens without apatite precipitation. After a week immersion in c-SBF, the AE patterns obtained from four-point bending test of HAp top coating specimens with and without bond coat clearly showed faster failure of the coating compared to those without c-SBF immersion. In addition, under c-SBF, the bond coating contributed to the retarded failure of the HAp top coating compared to that without bond coat. From XRD analysis, the as-sprayed layer composed of HAp coexisted with CaO. After c-SBF immersion, CaO dissolved into c-SBF and the as-sprayed HAp top coating changed to bone-like apatite which might contribute to the faster failure of the coating.