Study On Properties Of Microplasma Sprayed Hydroxyapatite Coatings

Hydroxyapatite(HA) is widely used as surface coatings on biomedical metallic implants because of its good bioactivity. Bioactive coating is made by microplasma spraying(MPS) technology in recent years, and relative study on it is seldom. HA coatings were deposited onto Ti6Al4V substrate by microplasma spraying (MPS) as well as by atmospheric plasma spraying (APS) in this research. Scanning electron microscopy (SEM) and energy-dispersive analysis (EDS) and X-ray diffraction (XRD) analysis are used to investigate the structure and properties of HA coatings. The relationship between spraying parameters and properties is studied. Heat treatment experiment rule is also discussed. HBSS incubation experiment is used to analyze the coating bioactivity. Results are as follows.1. Microstructure and phases of microplasma spraying HA coatings are influenced by spraying distance, current and gas flow rate. The decrease of current, spraying distance and increase gas flow rate could increase the crystallinity which could exceed 90% with a decrease of the impurities. The impurities only include TCP without CaO or TTCP which are included in APS coatings, and small power, low spraying speed and pure Ar may be the main reason.2. After heat treatment the crystallinity of MPS coatings increase clearly which increase with temperature rising, and amorphous phase and impurities convert to HA. OH- and PO4 have resumed their integrity which is accordance with APS coatings. CaO is still stay in APS coatings after heat treatment. Nucleation, grow and diffusion take place. Crystal average size grow along with temperature rising. It may be suitable to keep at 600~700℃for 3 hours for HA coatings.3. The functionally graded coating combined with super low crystallinity layer and lower high texture layer satisfied the need of rapid apatite layer forming speed in early stage and long term stabilization after being embedded.4. The functionally graded coating has good bioactivity in HBSS. New bone-like layer can form on its surface like the same with APS coating.