Influence of different substrate temperatures on coating properties in the coating of Ti6Al4V alloy with HA

The bonding of the implant to the surrounding tissue after implantation of Ti6Al4V alloys is important for the stability of the implant. For this purpose, Ti6Al4V alloys are coated with hydroxyapatite (HA) which is a bioactive material by thermal spray processes. In the HA coatings produced by thermal spraying systems, HA is exposed to thermal decomposition during spraying, which causes different phases to coexist. Also, amorphous phase is frequently observed in these systems. The presence of different phases and amorphous structure increases the dissolution rate by affecting the dissolution behaviour of the coatings in the body. Rapid dissolution increases the concentration of calcium ions that cause negative effects on the surrounding tissues. Therefore, in this study, the effects of different substrate temperatures and different thermal spray production methods were investigated in order to increase the stability and strength of the coatings in the body. As the coatings were obtained by accumulation of the splats, splats were produced on the Ti6Al4V substrate by flame and plasma spray methods at different substrate temperatures. With these splats, changes of microstructures, phase structures and dissolution in vitro conditions were determined according to the substrate temperature and production method in the vicinity of the bottom of the coating. According to the results, it has been determined that the rate of dissolution of the coating decreases with the increasing substrate temperature and plasma spray method is the most suitable production method for HA coatings. With respect to these results, coatings were produced at two different substrate temperatures by using the determined parameters in the plasma spray method and the effect of substrate temperature on the adhesion strength of coating was determined. The result of the study shows that the adhesion strength of the coatings increases with increasing the substrate temperature.