Microstructural study of plasma sprayed hydroxyapatite coatings

Purpose: The aim of this study is to present microstructure and mechanical properties of hydroxyapatite coatings sprayed by means novel plasma system with axially injection of powder. Design/methodology/approach: Coatings were deposited with Axial III plasma spraying system and examined by SEM, XRD and by a nanoindentation technique (Nanovea) with a Berkovitz indenter. Surface of coatings was analysed by means of a Talysurf CCI-Lite non-contact 3D profiler. Findings: This study shows the microstructure and mechanical properties of hydroxyapatite coatings (HA) obtained by plasma spraying from the powder with a cauliflower-like high porous structure consisting of nanograins with dimension below 100 nm. The cross-section of plasma sprayed HA coating reveals lamellar structure containing pores in the interior of the lamellae. Moreover, between lamellae, some microcracks were detected. Hardness and elastic modulus measured by nanoindentation were found to be around 0.085 and 6.82 GPa respectively, what was comparable with HA coatings sprayed by a modified cold spray system. Both XRD patterns are practically identical, so no new phases were created in hydroxyapatite coating in comparison with feedstock powder during the spray process. High values of a geometry of HA coating; maximum peak height, maximum pit height and maximum height confirmed significant roughening of a surface, which is a result of the interaction of melted powder grains with the surfaces during the plasma spraying. Research limitations/implications: Obtained properties of coatings will be the base for comparison with suspension plasma sprayed coatings. Practical implications: Hydroxyapatite coatings deposited by means novel plasma system are designated for spraying implants. Originality/value: Properties of hydroxyapatite coatings plasma sprayed with novel axially injection of powder.