Low-Temperature-Sintered Fe-Based Self-Lubricating Composites Reinforced with Graphite and Graphene Oxide

Self-lubricating iron-based composites produced by powder metallurgy are promising materials for reducing friction and improving component durability under dry-sliding conditions. In this study, three composites reinforced with graphite and/or graphene oxide (Fe10%Gr, Fe10%GO, and Fe5%Gr5%GO) were fabricated to evaluate the influence of solid lubricants on densification, hardness, and tribological behavior. Powders were uniaxially compacted at 500 MPa and low-temperature-sintered at 880 °C under an argon atmosphere. The tribological performance was assessed by pin-on-disk tests against an AISI 52100 steel ball. Pure Fe exhibited the highest hardness (approximately 97 HV) and a final porosity of 17.5%, whereas the lubricant-containing composites showed porosities ranging from 17.3% to 22.8% and lower hardness values of 45–60 HV. Despite the reduction in hardness, all lubricant-containing compositions decreased the coefficient of friction relative to pure Fe (~0.33). Fe10%Gr and Fe5%Gr5%GO exhibited the lowest friction coefficients, reaching ~0.08 and ~0.05, respectively, while Fe10%GO showed the highest wear rate (~1.1 × 10−2 mm3/Nm). Among the compositions studied, Fe5%Gr5%GO showed the best friction–wear balance among the self-lubricating formulations, combining low friction and moderate wear due to a surface synergy where graphite promotes continuous low-shear lubrication while GO promotes the formation of a more compact and resilient protective tribolayer.