Tribological characterization of epoxy hybrid nanocomposite coatings reinforced with graphene oxide and titania

Abstract

Epoxies in the form of bulk and coatings have been used throughout the years for a wide spectrum of applications in industries. However, the application of epoxies in demanding tribological applications is often limited by the properties of the pristine epoxy matrix such as low load bearing capacity under severe p-v regimes combined with low thermal conductivity values. In this study, the load bearing capacity of the pristine epoxy coating system applied onto non-textured, plasma treated mild steel substrates was first evaluated under dry sliding conditions. Wear tests were conducted using a ball on disk configuration with a grade 440C hardened stainless steel ball with a diameter of 6.3 mm and a hardness of 62 HRC, as the counterface. Graphene oxide (GO) fillers in varying concentrations of (0.25, 0.5, 1 and 1.5 wt%) were added to the pristine epoxy matrix to produce Epoxy-GO nanocomposite epoxy coatings and tribological evaluation was carried out. Tribological tests revealed that the addition of GO nanoparticles at 0.5 wt% filler loading led to a significant improvement in wear life (~6.5 times) when compared to the pristine epoxy system. In the second phase of this study, titania (TiO2) fillers were added to the optimized epoxy-0.5 wt% GO nanocomposite coating to produce GO-TiO2 hybrid nanocomposite epoxy coatings and tribological evaluation was carried out. However, tribological tests did not indicate any significant increase in the wear life after the addition of TiO2 as compared to the Epoxy-GO nanocomposite epoxy coatings. A detailed study of coating failure and wear mechanisms at significant datapoints were carried out using a combination of techniques namely coefficient of friction graphs for wear life, SEM for wear track imaging, EDS for elemental analysis of the wear track to establish failure, optical profilometry and counterface imaging using optical microscopy.