Crystallite orientation and anisotropic strains in thermally sprayed hydroxyapatite coatings

Thermally sprayed hydroxyapatite powders and coatings have been studied using X-ray powder diffraction and scanning electron microscopy. Preferred orientation of the crystallites has been found on a number of coated plates using X-ray powder diffraction, and full profile fitting of the patterns from the extracted powders indicates anisotropically thermally strained crystallites. This is a result of rapid crystal regrowth and associated thermal gradients on deposition. Electron micrographs of some coatings show a consistent picture of columnar crystallites orientated perpendicular to the substrate surface.