Chemical Inhomogeneity of Plasma Sprayed Hydroxyapatite Coatings

Hydroxyapatite(HA) coatings were fabricated using plasma spraying method.The samples were polished along the direction parallel and vertical to the coating surface,respectively.Microstructure,element distribution and phase composition of the surface and cross-section of coaings were examined by a JXA-8800R electron probe microanalyser(EPMA) with a Link ISIS300 energy spectrum analyzer and a D/max-γB X-ray diffractometer(XRD).The results show that there exists chemical inhomogeneity in terms of chemical composition and phases in the coatings,corresponding to color differences in back scattering electron(BSE) images.The micro-regions with low P and low O contents are composed of amorphous,decomposed and recrystallized Ca-P phases.The difference in moltening degrees of HA particles during plasma spraying results in the inhomogeneity.Heat treatment eliminats the chemical inhomogeneity but results in the formation or spreading of cracks within the coatings.