Development of hydroxyapatite coatings by solution precursor plasma spray process and their microstructural characterization

Solution precursor plasma spraying (SPPS) is a promising method of obtaining coatings with unique microstructural features. The present study reports about the development of hydroxyapatite (HA) coatings by SPPS using water-based calcium-phosphate solution and about the analyses of their microstructure. X-ray diffraction (XRD) analysis showed that HA was the major crystal phase of the coatings, being present in the range from 95% to 98%. The coatings of greater HA content were obtained while spraying using shorter spray distance. The coating crystallinity ranges from 24% to 69% depending on the temperature at deposition. An increase of the temperature results in greater crystallinity. The obtained coatings' microstructures may be described by dome-like surface and by the columnar-like cross-section when using precursor with low concentration. The use of concentrated solution precursor results in cauliflower-like structures composed of agglomerated fragmented shells and fine spherical particles. The possible phenomena occurring in droplets in contact with the plasma jet and the coating buildup mechanisms were tentatively explained. (C) 2016 Elsevier B.V. All rights reserved.