Effect of graphene coating on modified and pristine carbon fibers on the tribological response of carbon fiber epoxy composites

Addition of graphene nanoplatelets (GNP) as nanofillers in carbon fiber reinforced polymer composites improves a range of mechanical properties e.g. flexural, tensile and fatigue. Multiple studies have reported that this occurs through the formation of a carbon-enriched interphase with intermediate properties between the epoxy, graphene and carbon fiber. However, even though GNPs act as a solid lubricant and have exceptional strength and thermal conductivity, the wear performance and failure mechanism of GNP-incorporated composites are still not understood. The current study aims to investigate the effect of GNP-coated-pristine as well as GNP-coated-oxidized carbon fibers on the wear performance of carbon fiber reinforced epoxy composites manufactured through vacuum-assisted resin transfer molding technique (VARTM). It has been found that specific wear rate and coefficient of friction were lower for GNPs added composites compared to pristine laminates and it was the least in the case of composites in which an optimum amount of GNPs was coated on oxidized carbon fibers. Moreover, smaller temperature within the specimens has been found during the wear test in the case of GNP-added laminates owing to the higher thermal conductivity of the GNPs. Worn surface morphology has shown formation of thin epoxy layers at lower number of cycles for all the laminates. Fiber breakage, debonding resulting in clean fibers and a large amount of wear debris has been seen on worn surfaces of pristine laminates. However, GNP-added laminates have shown less wear debris and enhanced fiber-epoxy bonding. The wear response has been correlated with the size of the interphase formed between the fiber and the epoxy.