Effect of post-deposition heat treatment on mechanical properties of thermally sprayed hydroxyapatite coating

Abstract

This paper mainly deals with the inner microstructure and mechanical performance of plasma sprayed hydroxyapatite (HA) coatings before and after heat treatment. The electron probe microanlyser shows that some regions with different contrasts exist in the as-sprayed coatings. Under the back scattering electron (BSE) model, the origin particles of HA are well melted, and there are the more inhomogeneites in the as-sprayed coatings. Heat treatment can eliminate the regions with different contrasts and improve the crystallinity of the coatings. Some coatings were immersed into 50 mL deionised water under constant 37°C condition for 20 days. After the immersion in the deionised water, new layers with dot like precipitates formed on the surface of the as-sprayed coatings and the inhomogeneities were eliminated. For as-sprayed coatings, the amount of precipitates on the surface of low crystalline coatings is larger than that of high crystalline coatings. For post-heat treated coatings, there are no other phases but β-Ca₂P₂O₇ precipitates along the cracks paths. The shear strength of as-sprayed coatings of low crystallinity is higher than that of high crystalline coatings. In this paper, post-heat treatment can improve the shear strength of coarse coatings but decrease that of fine coatings.