The changes in the surface morphology of graphite foils with different densities (1.0, 1.3, and 1.6 g/cm3) based on different fractions of purified natural graphite with particles of 160–200 μm in size were studied before and after tribological tests. The research focuses on analyzing the mechanisms of destruction and delamination of surface and bulk layers of material, as well as assessing the influence of density on the formation of a protective friction film. Tribological tests were carried out under conditions of reciprocating motion at sliding frequencies of 0.1 and 1.0 Hz. It was found that with increasing material density, the friction coefficient decreases, especially at low sliding frequency. This is due to more intensive delamination of the surface layers of samples with densities of 1.3 and 1.6 g/cm3, which facilitates the exfoliation of graphite particles and the formation of a dense carbon-based film on the counterbody. Scanning electron microscopy was used to study the structural changes in both the original and worn surfaces. It was shown that at a high sliding frequency, the destruction processes proceed more intensively, especially in dense samples, but they retain the structure stability in deep layers. Analysis of the chemical composition of the counterbody surfaces confirmed the presence of a significant amount of carbon transferred during friction. The most uniform and dense friction film is formed when using graphite foil with a density of 1.6 g/cm3. This film acts as a solid lubricant, reduces the friction coefficient, and protects the metal surface from wear. The obtained data demonstrate that an increase in the density of graphite foils provides better tribological performance due to an optimal combination of strength and self-lubricating ability.
Bukovskiy et al. (Mon,) studied this question.
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