Structure and phase composition of hydroxyapatite plasma coating

Changes in the structure and phase composition of the hydroxyapatite (HA) plasma coating were established during deposition at the initial temperatures of 20 and 550°C of the titanium substrate and a deposition distance of 95 and 150 mm. The structure of HA coatings was analyzed by SEM and optical microscopy. DSC analysis established the transition temperatures of HA coatings to the equilibrium state. When deposited on a substrate with an initial temperature of 20°C at a deposition distance of 95 mm, a nanostructure with a crystallite size of 21 nm is recorded in the HA coating. When the deposition distance increases to 150 mm, the nonequilibrium phase composition increases, the crystallite size decreases to 12 nm, the HA content decreases from 72 to 61%, the TTCP content decreases from 10 to 5%, and the α-TCP content increases from 17 to 30%. A nonequilibrium nanostructural state passes into a more equilibrium state with the release of heat at temperatures of 615–727°C in DSC studies. The high-temperature α-TCP phase is not recorded when the coating is deposited onto a substrate with an initial temperature of 550°C at a deposition distance of 95 mm, the TTCP content increases by two times, the size of the HA phase crystallites reaches 36 nm, and their size in the sprayed powder is 75 nm. The HA coating has a dendritic microstructure and has no thermal effect during DSC heating at an initial substrate temperature of 550°C.