Tribological Performance of Graphene-Based Sacrificial Coatings

Graphene solution was spin coated onto an aluminum substrate to investigate its tribological behavior compared to bare 6082–T6 aluminum alloy. The coefficient of friction (COF) was measured for varying loads (1–5 N) and sliding speeds (0.05–0.25 m/s) using a pin-on-disk tribometer in a ball-on-flat configuration. Results indicated that, under all tested conditions, the graphene coating reduced the COF by more than 70–80% compared to uncoated aluminum. Specifically, at 0.25 m/s and 1 N, the COF decreased from approximately 0.63 for uncoated aluminum to about 0.13 for the coated sample. The samples were analyzed using optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), providing insights into morphology and composition. Furthermore, the coated samples exhibited a stable friction regime, with COF values consistently in the range of 0.10–0.15, while uncoated samples showed higher and more fluctuating values between 0.40 and 0.60. The graphene coating reached steady-state conditions within the first 50 m of sliding, in contrast to the pronounced running-in behavior of uncoated aluminum. SEM and EDS analyses confirmed the formation of a graphene transfer layer on the counterface, which maintained low friction even after partial coating removal. Additionally, the average coating thickness was approximately 15 μm, and the coating significantly reduced adhesive wear and material transfer, demonstrating its effectiveness as a sacrificial, self-lubricating tribological layer.