Size-dependent tribological performance of graphene-reinforced Al matrix composites

The incorporation of graphene into Al matrix composites has emerged as a promising approach to enhance wear resistance; however, the impact of graphene size on tribological behavior remains inadequately understood. In this study, graphene oxide precursors with three distinct lateral sizes were synthesized and incorporated into an Al matrix via hetero-agglomeration, followed by in situ thermal reduction during spark plasma sintering. This approach enabled the creation of structurally comparable graphene/Al systems, facilitating the isolated evaluation of the lateral size effects. Comprehensive microstructural and tribological analyses revealed that the composite reinforced with medium-sized graphene exhibited the lowest coefficient of friction, narrowest wear track, and most stable worn surface. These improvements are attributed to the formation of continuous and well-bonded graphene networks, which effectively reduce Al abrasion and oxidation. In contrast, small-sized graphene provided insufficient surface coverage, whereas large-sized graphene exhibited stacking and detachment, both of which compromised the tribological performance. Unlike most previous studies that primarily focused on graphene content, this work systematically investigates the role of graphene lateral size. A wear mechanism model was further proposed to describe the size-dependent frictional behavior. Overall, these findings underscore the critical role of the lateral size of graphene as a design parameter for optimizing the tribological performance of next-generation wear-resistant metal matrix composites. • A structurally comparable graphene/Al composite system with tailored lateral sizes was established. • Medium-sized graphene enabled continuous and well-bonded interfacial networks with lowest coefficient of friction. • Small-sized graphene provided poor coverage, while large-sized ones stacked and detached, worsening wear behavior. • A wear mechanism model was established to describe the size-dependent frictional behavior.