Impact of post-heat-treatment on the surface-roughness, residual stresses, and micromorphology characteristics of plasma-sprayed pure hydroxyapatite and 7%-Aloxite reinforced hydroxyapatite coatings deposited on titanium alloy-based biomedical implants

Abstract

The biocompatible hydroxylapatite (Ca10(PO4)6(OH)2) (HA) coating is usually depositing on the titanium substrate to enhance the healing process of implant and to isolate it from the harsh body environment. However, poor mechanical properties of HA restrict its usage for orthopedic applications like hip and knee joints which have to bear the load. The biocompatibility is provided by HA and mechanical strength by the addition of reinforce with HA. Thermal post treatments have been mostly utilized to enhance the morphological and physicomechanical characteristics of as-deposition coatings. In the present research, the emphasis has been laid to analyze the outcome of thermal-processing on phases of hydroxyapatite in coatings developed by plasma spraying process. The surface-morphology of as-sprayed and thermally-processed, HA coated samples was studied using Scanning electron microscope (S.E.M.), Elemental-mapping, X-ray diffraction analysis (X.R.D.), and Fourier-transform infrared (F.T.-I.R.) spectroscopy techniques. The outcomes achieved from the X.R.D. analysis of the hydroxylapatite-coated samples after thermal-treatment reveal the formation of crystalline structure at 750 °C with some traces of CaO. Moreover, when the heat treatment was further done at 950 °C, the unwanted CaO was totally eliminated and coating with crystalline structure was obtained. No substrate element is visible in the X-ray mapping of coatings. The presence of ultrafine particles was observed on both substrates after the heat treatment of coatings at specified temperatures for 2hr in air. These ultrafine particles have the capability to bond with the bone and also helps for bone in-growth on their surfaces.