Synergistic friction and wear reduction in CuSn10-modified basalt fiber-reinforced epoxy composites via protic ionic liquid and graphene nanolubrication

Basalt fiber-reinforced epoxy (BFRP) composites combine a favorable strength-to-weight ratio with relatively low cost, which makes them attractive for structural applications. However, the epoxy matrix has limited abrasion resistance, and this restricts how well these composites perform under sustained sliding contact. In this study, two autoclave-processed BFRP variants were tested: an unfilled composite (60 wt% basalt fiber) and a hybrid composite modified with 10 wt% CuSn10 bronze powder. The two samples were evaluated under dry sliding and under lubrication with four 2-hydroxyethylammonium (2-HEA)-based protic ionic liquid (PIL) nanofluids two used neat (MSu, MCi) and two dispersed with 0.1 wt% graphene (MSu + 0.1%G, MCi + 0.1%G). Pin-on-disc tests were performed under a normal load of 10 N and a sliding speed of 0.25 m·s⁻ 1 , and worn surfaces were characterized by SEM–EDS. A full factorial experimental design was employed to systematically assess the effects and interactions of composite material, PIL anion type, and graphene addition on the coefficient of friction and specific wear rate, followed by statistical evaluation using General Linear Model (GLM) ANOVA. The results showed that all four PIL nanofluids significantly reduced the friction coefficient, with a decrease of 83–94% compared to dry sliding. Moreover, the specific wear rate was reduced by 14% to over 99%, although the highest values were close to the measurement limit and should be interpreted with caution. The graphene-dispersed citrate PIL (MCi + 0.1%G) yielded the lowest wear rate for both composite variants and the lowest friction coefficient for the CuSn10-modified composite. On the other hand, the graphene-dispersed succinate PIL (MSu + 0.1%G) gave the lowest friction coefficient for the unfilled composite. Notably, the CuSn10-modified composite showed a wear rate comparable to the best-lubricated unfilled composite even under dry sliding. However, the improvement is also due to the correspondingly lower content of basalt fibers (50 vs. 60 wt%) in the CuSn10-modified variant. It is therefore a joint effect of lower fiber content and CuSn10 addition, not an isolated CuSn10 effect. It is still consistent with a load-bearing role of bronze particles, independent of lubrication, which was not directly shown in this study. The statistical results revealed significant Material × Graphene and Anion type × Graphene interactions, as well as a significant three-way Material × Anion type × Graphene interaction for the specific wear rate, providing statistical evidence of a synergistic dependence of the tribological performance on composite composition, PIL chemistry, and graphene addition. It is acknowledged by the authors that this is the first report of its kind to combine a metallic load-bearing filler (CuSn10) with graphene-dispersed protic ionic liquid nanolubricants on a basalt fiber-reinforced polymer composite, evaluated under a unified, statistically validated experimental framework. These findings establish this combined material–lubricant strategy as an effective approach for improving the tribological durability of basalt-fiber composites in sustained sliding applications.