Morphological, structural and mechanical characterization of cold sprayed hydroxyapatite coating

Abstract

The present paper investigates the deposition behavior of cold spraying agglomerated hydroxyapatite (HA) particles on stainless steel (SS) and HA substrates; for that purpose, the surface morphologies and cross-section microstructures of splats were investigated and compared to that of original HA particles. Full characterization of the coating was performed through the evaluation of (i) phase constitutions, crystallographic structure and composition, and coating/substrate interface as well as (ii) nanohardness of the powder, microhardness, tensile strength and the abrasive wear properties of the coating. HA splats on both substrates exhibited cap-like shape morphology with rough surface, and had some ring grooves on surface and some radial stripes on periphery composing of tiny HA granules. The cross-section of HA splats presented an asymmetric ellipsoid morphology with a flat bottom surface and convex up surface as well as compact area near bottom interface. Bonding of splats/substrate interface was related to the splats size and substrate materials. CS HA coating possessed a dense and homogeneous microstructure with reduced pores and crystal size, similar chemical structures, phase constitutions and chemical compositions to original powder. These microstructure evolutions were related to the deformation behavior of HA splats, i.e. radial spreading and compacting in impact direction by the un-continuous moving of agglomerates or granules in low temperature. Microhardness, tensile strength and the abrasive wear rate of the coating were 59.0 ± 5.6 kg/mm2, 10.9 ± 1.1 MPa and 1.3 ± 0.2 × 10−1 mg/(m·N), respectively.