Effect of Morphology of Electrophoretically‐Deposited Carboxylated Graphene Over Carbon Fibers on the Tribological Properties of Epoxy Composites

ABSTRACT

Graphene deposited carbon fiber epoxy composites show enhanced tensile properties through improved interfacial strength; however, improved wear resistance is also essential for demanding applications such as bearing bushings in aggressive environments. In the present study, carboxyl‐functionalized graphene (G‐COOH) was electrophoretically deposited onto carbon fiber fabrics to study tribological properties of such composites. Carbon fiber fabrics coated with particle Type (0.1, 0.4, 0.8 wt.% G‐COOH), and film type (1.1 wt.% G‐COOH) graphene (GCF) were used to fabricate composites via the VARTM technique. Subsequently, ball‐on‐disc tribological tests were performed at 500, 10,000, 15,000, and 25,000 revolutions for all GCF composites, along with pristine carbon fiber (PCF) composites. Additionally, temperature sensor was mounted on the sliding ball to record the temperature evolution. The coefficient of friction (COF) of all composite specimens over 25,000 sliding revolutions exhibited four distinct stages: an initial rapid increase followed by a slight reduction (i.e., initial COF peak), a gradual rise associated with epoxy layer formation, a steady plateau during stable sliding, and a final transition to a lower stable region. Furthermore, analysis of the friction behavior and scanning electron microscope images at different sliding revealed the progressive evolution of the material removal mechanisms, including the formation of an epoxy layer, its gradual growth, subsequent wear and debonding of the epoxy layer, exposure of carbon fibers, and eventual fiber wear during prolonged sliding. GCF composites showed a faster initial rise and subsequent sharp decrease in COF, attributed to graphene platelet edges, increased interphase thickness, and surface roughness from the transverse graphene morphology. Beyond the transition region (~10,000–15,000 revolutions), all GCF composites exhibited lower COF than PCF, owing to enhanced interphase strength and graphene's solid‐lubricating effect. All GCF composites exhibited lower wear volume and specific wear rate compared to the PCF composite. Notably, the 1.1 wt.% GCF composite showed the highest resistance to wear. SEM imaging of worn surfaces revealed relatively smoother worn surfaces in GCF composites compared to PCF composites. The lower temperatures observed for the GCF composites than the PCF composite may be attributed to faster heat dissipation into the composite, facilitated by the presence of graphene platelets.