Mechanical properties, microstructural characteristics and in-vitro behavior of APS-sprayed nanostructured and conventional hydroxyapatite coatings

Nanostructured and conventional hydroxyapatite (HA) feedstocks were evaluated to determine the effects of feedstock structure on the processing, properties and performance of coatings produced by atmospheric plasma spraying. The structure of the feedstocks was characterized using scanning electron microscopy (SEM). It was found that the nanostructured feedstock particles were formed by an agglomeration of nanostructured fibers having dimensions of less than 500 nm in length and below 100 nm in width. The average particle temperatures and velocities were measured during plasma spraying and found to be ∼2650°C and ∼315 m/s for the both feedstocks. The mechanical, microstructural and biocompatibility characteristics of coatings deposited on Ti-6Al-4V substrates were evaluated. The hardness was measured using Vickers indentation. The bond strength was determined via a tensile adhesion test. Microstructural characteristics of the coatings and their porosity levels were evaluated using SEM and image analysis. Phase analysis was carried out via X-ray diffraction (XRD) and aided by energy-dispersive X-ray analysis (EDS). The in-vitro behavior of these coatings was investigated in a simulated physiological solution in an attempt to simulate the environment of an implant in the human body.