The Mechanical Properties and Biocompatibility of Functionally Graded Coatings(FGC) of Hydroxyapatite(HA) and Metallic Powders - Functionally Gradient Coatings of Thermal Spray in Air

Abstract

This work presents functionally graded coatings (FGC) of hydroxyapatite (HA) and metallic powders on Ti-6Al-4V implants using plasma spray coating method. HA has been the most frequently used coating material due to its excellent compatibility with human bones. However, because of the abrupt changes in thermomechanical properties between HA and the metallic implant across an interface, and residual stress induced on cooling from coating temperture to room temperature, debonding at the interface occurs in use sometimes. In this work, FGC of HA and Ti or Ti-alloy powders is made to mitigate the abrupt property changes at the interface and the effect of FGC on residual stress release is investigated by evaluating the mechanical bond strength between the implant and the HA coating layers. Thermal annealing is done after coating in order to crystallize the HA coating layer which tends to have amorphous structure during thermal spray coating. The effects of types and compositional ratio of metallic powders in FGC and annealing conditions on the bond strength are also evaluated by strength tests and the microstructure analysis of coating layers and interfaces. Finally, biocompatibility of the coating layers are tested under ISO 10993-5.