Effect of heat treatment on the microstructure of plasma-sprayed hydroxyapatite coating.

One of the claimed benefits of plasma-sprayed hydroxyapatite coatings on metal prostheses is the generation of enhanced bone bonding. However, plasma-sprayed hydroxyapatite undergoes a range of transformations during spraying, and the final microstructures produced are complex, with a variety of phases present. The microstructures of plasma-sprayed hydroxyapatite coatings on titanium alloy substrate which have been subjected to post-heat treatment at 950 degrees C have been characterized using transmission electron microscopy. It was demonstrated that heat treatment can modify the coating microstructure and improve adhesion between coating and substrate. The results of chemical analysis revealed an increase in the Ca:P ratios, accompanied by the transformation of calcium phosphate phases from amorphous to crystalline. These transformations are related to phosphorus diffusion into the titanium alloy substrate, which results in the formation of a Ti3P phase.