Fabrication of Novel Hydroxyapatite/Titanium Composite Coating Using rf Reactive Plasma Spraying

Abstract

Novel hydroxyapatite (HAp) / titanium (Ti) functionally gradient composite material has been developed by new plasma spraying technique using radio-frequency (rf) thermal plasma spraying method. Plasma sprayed HAp coatingon titanium substrate has been used for hip prostheses and dental implant, however, there is a in vivo problem of loosening. HAp coatings with sufficient thickness and excellent adhesion to the Ti substrate have been strongly demanded. The plasma-sprayed process is specified by the associated processing parameters (particle size of HAp powder, carrier gas rate, plasma power, and spraying time et al.) where these influence the properties of the resultant deposits. To improve the stability in vivo, the highly oriented HAp coatings were prepared by rf. thermal plasma method, and the degree of this orientation was little affected by RF input power while it showed a tendency to increase with an increase in the substrate temperature during spraying. To improve bond strength of HAp coatings to titanium substrate, the HAp/Ti functionally gradient composite coating on Ti substrates was successfully prepared. The ratio of HA and Ti powders supplied into the plasma was precisely controlled by two micro-feeders so as to change the coating composition from Ti-rich to HA-rich toward the upper layer, and the thickness of HAp/Ti composite layer was 50 μm. Above that, only HAp was applied to produce HAp layer 100 mm thick on the top. The bond strength between HAp layer and Ti substrate was remarkably improved. It was also found to be depended on the partial nitriding of Ti deposits using rf reactive plasma spraying. When sprayed with 1.8% N 2 added at 27 kW, the bond strength of the obtained HA/Ti composite coatings reached 65.3 MPa. From the results of XRD and SEM analysis, titanium nitrides were formed in the titanium deposits sprayed with plasma gas containing N 2 .