Heat and hydrothermal treatments on the microstructure evolution and mechanical properties of plasma sprayed hydroxyapatite coatings reinforced with graphene nanoplatelets.

Abstract

Recent demands in clinical applications drive a large amount of research to plasma sprayed hydroxyapatite (HA) composite coatings. Herein, graphene nanosheet (GNS) reinforced HA coating was fabricated using plasma spray, the effect of heat and hydrothermal treatments (hereafter referred to as thermal treatment) on microstructural evolution and mechanical properties of the composite coating were investigated. Thermally treated GNS/HA coating not only exhibited ~47.1% improvement in HA crystallinity and more denser microstructure, but also displayed increased surface roughness (3 times of that of the as-sprayed sample) due to the fact that GNSs facilitated HA nanoparticle precipitation on the coating surface. Fracture toughness of the as-sprayed HA coating increased by up to ~44.1% at 2.0 wt% GNSs owing to GNS pullout, GNS bridging and arresting of crack propagation by the embedded GNSs. As for thermally treated HA coatings, crack propagation arrested by the sintered regions was found to act as an important toughening mechanism, but thermal treatment introduced more structural defects into the GNSs and led to the reductions in their length and thickness, resulting in negligible enhancement in toughness of the GNS/HA coating.