Effect of heat treatment on performance of hydroxyapatite coatings immersed in simulated body fluid

Abstract

In this paper, the effect of heat treatment on the performance of hydroxyapatite (HA) coatings immersed in simulated body fluid (SBF) is researched. The electron probe microanalyser results show that different contrast appears on the planar microstructure images, and chemical inhomogeneity exists, in the plasma sprayed HA coatings. Heat treatment can eliminate the inhomogeneity, increase crystallinity of the coatings and make the element distributions tend to be homogeneous. The X-ray diffraction results show that the decomposed phase decrease, indicating that some recrystallinity chemical reactions occurred during heat treatment. The shear adhesion test shows that the bonding strength of the high crystallinity coatings increased, while the low crystallinity coatings significantly decreased (p<0⋅05) after heat treatment. However, bonding strengths of all the coatings markedly decreased (p<0⋅05) after immersion in 0⋅5SBF for 4 weeks. The scanning electron microscopy results show that the cracks, pores as well as boundaries of unmelted particles in the coatings are the origins of the rupture. There are some needle like nanocrystals distributing on the pores at the fractures of as sprayed coatings, while needle like crystals are not found at the fractures of heat treated coatings.