Enhanced Tribological Performance in Simulated Body Fluid and Erosion Resistance of Plasma-Sprayed Hydroxyapatite Coatings Reinforced with Graphene Nanoplatelets

Abstract

Hydroxyapatite (HA) coatings are commonly used for biomedical implants due to their biocompatibility; however, their poor tribological properties, such as high wear rate and coefficient of friction (CoF), limit their long-term performance in body fluid environments. The tribological performance of plasma-sprayed HA coatings reinforced with graphene nanoplatelets (GNPs) at concentrations of 0, 1 wt.%, and 2 wt.% was evaluated in a simulated body fluid (SBF) environment against an alumina (Al2O3) ball. The HA matrix containing a uniformly dispersed 2 wt.% of GNPs exhibited a significant reduction in wear weight loss (76%), wear rate (84%), coefficient of friction (CoF) (39%) in simulated body fluid. These improvements are primarily attributed to the lubrication effect provided by the peeled-off graphene layers from the GNPs surface. FE-SEM analysis of the worn surface revealed mechanisms such as GNP bending, GNP pull-out, and fragmented GNPs, which contributed to the enhanced wear resistance of the coating. The lubrication induced by the presence of GNPs was identified as the main factor responsible for the lower CoF of the worn surface. Additionally, the HA-2G composite coating exhibited the lowest erosion rate (3 g/kg). This decrease in the erosion rate can be attributed to the enhanced densification of the composite coating. The findings have direct implications for orthopedic and dental implant technologies, where improved tribological performance and longevity of implant coatings in body fluid environments are critical.