Deposition of hydroxyapatite and tricalcium phosphate coatings by suspension plasma spraying: Effects of torch speed

This research focuses on the deposition of hydroxyapatite (HA) and tricalcium phosphate (TCP) coatings produced by suspension plasma spraying (SPS) using in-house liquid feedstock suspensions. The work studied the effects of torch speed on the thickness, microstructure, and crystalline composition of the coatings. SPS allowed the deposition of HA and TCP coatings with thickness between 28 and 90 μm. The coatings presented lamellar microstructure with complex porosity between the splats. Micropores ranging from 0.2 to 6 μm and close mesopores, from 8 to 45 μm, had a spherical morphology and were homogenously distributed within the coatings. Water evaporation during SPS allowed the retention of pure and crystalline HA coatings. In contrast, the presence of water molecules led to the formation of HA as a secondary phase in the TCP coatings, which formed α-TCP as the major component due to the high temperature reached by the powder during deposition.