Effect of Varying Stand-off Distance on Tribological and Mechanical Properties of Plasma Sprayed Hydroxyapatite Coated Metallic Substrates

Plasma spray technique is commonly used for the fabrication of hydroxyapatite (HA) coating for bio implants. Out of various process parameters in plasma spray technique, stand-off distance is one of the most important parameter which affects tribological and mechanical properties of the substrate. In the present work, HA powder was plasma sprayed onto Titanium grade 2 and Titanium grade 5 metallic substrates by varying standoff distance. Wear test was carried out to determine coefficient of friction and wear weight loss in the presence of simulated body fluid having a common pH of 7.25 similar to human blood plasma. The scanning electron microscopy and X-ray diffraction were used for characterization of microstructures and phase composition of coating respectively. Results have shown that HA coating obtained at 230 mm stand-off distance exhibits hardness and anti-wear characteristics as compared to coatings with stand-off distance of 180mm and 280 mm. This may be attributed to lower porosity and dense structure at a stand-off distance of 230 mm. The main wear mechanisms on the coating's wear track were found to be abrasive and adhesive.