The Tribological Performance of Fine-Grained Isotropic Graphite Under Synergistic Variable Conditions

Abstract

Abstract. This study systematically investigates the tribological behavior of fine-grained isotropic graphite under synergistic variable conditions, addressing a critical knowledge gap regarding its performance in extreme conditions. While graphite is a promising high-temperature solid lubricant, its utility is limited by environmental dependencies. Our research reveals that the tribological performance of fine-grained isotropic graphite depends on the formation and stability of interfacial tribofilm rather than its bulk properties. Comprehensive reciprocating test against 440C stainless steel counter bodies explores friction and wear across varied temperatures (room temperature, 100 °C, and 300 °C), load, and velocities. Advanced characterization including X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy, optical profilometry, and Raman spectroscopy explains the underlying wear mechanisms. Performance paradox was identified under high-load conditions, failure at 100 °C, while low friction (µ ≈ 0.035) and low wear (0.718 mm3) performance was observed at 300 °C. Raman analysis confirmed that the 100 °C failure was due to mechanical refinement of graphite into highly disordered carbon debris following moisture desorption. The low wear and friction performance at 300 °C load ramp test was due to the formation of a stable ordered graphitic transfer film. However, under high-velocity conditions, frictional heat, a second distinct failure mechanism, causes tribo-oxidation, which degrades the protective film. These findings underscore that controlling the interfacial temperatures is the most important parameter for the sustained low-friction and wear performance. This work provides insights for optimizing graphite's application in demanding tribological environments.