Papers by Author: A. Rakngarm Nimkerdphol

Abstract: Plasma sprayed Hydroxyapatite (HAp) coating on commercially pure titanium (cp-Ti) is widely used as implant materials. In this study, fatigue behavior of as-sprayed HAp top coat with HAp/Ti bond coat specimen under ambient environment (A-HTi) as well as under simulated body fluid, SBF, environment (I-HTi) at 36.5°C was investigated by four point bending fatigue test at a stress amplitude of 170 MPa under various frequencies. In order to investigate apatite precipitation during fatigue loading, the test specimen was immersed in SBF at 36.5°C during the fatigue test. For comparison, the test specimen was immersed in SBF at 36.5°C for a day to a week without fatigue loading and then the fatigue test of the immersed specimen was carried out under ambient environment (I-A-HTi). The fatigue loading would not influence the apatite precipitation in the HAp coating layer of the specimen. The fatigue lives of the I-HTi and I-A-HTi specimens were shorter compared to that of A-HTi specimen. The shorter fatigue lives of the I-HTi and I-A-HTi specimens would result from the attack of SBF on titanium substrate. However, the apatite precipitation in the coating layer up to one week immersion did not significantly influence the delamination between HAp top coat and cp-Ti substrate under the bending fatigue.

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.