Papers by Author: Teerawat Loanapakul

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.

Abstract: In the conventional hydroxyapatite (HAp) coating, the surface of commercially pure titanium (Cp-Ti) is blasted with Al2O3 grid-blasting powders and then plasma-sprayed with HAp. To improve the adhesive strength of HAp coating, the grid-blasting with Al2O3 powders and subsequently wet-blasting by HAp/Ti mixed powders were applied on Cp-Ti substrate at ambient temperature. On the wet-blasted surface of Cp-Ti, two-layers of coating composed of HAp/Ti bond coat and HAp top coat were deposited by plasma spraying. Both types of HAp-coated specimen could survive up to 107 cycles without spallation of HAp coating at the stress amplitude of 120 MPa under four point bending fatigue test. In order to clarify mechanical failure behavior of the coatings and Ti substrate, acoustic emission (AE) signals during the entire fatigue process were observed. Relationship between AE behavior and cracking process of coated specimen was evaluated. HAp top coat with HAp/Ti bond coat strongly improved the adhesive and cohesive strength, where dense AE signals occurred at the early stage of fatigue test corresponded to plastic deformation of Ti substrate and micro-cracks in coated layers. AE signals occurred at the final stage corresponded to crack propagation in coated specimen and spallations of coated layers.