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- 2015 (5) (entfernen)
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- Graphite (3)
- Hydrogen (2)
- Polyimide (2)
- Tribofilm (2)
- Vacuum (2)
- Ball milling (1)
- Composites (1)
- Cross-sectional TEM (1)
- Friction (1)
- Graphit (1)
The composition and nanostructure of a beneficial tribofilm formed during sliding of a hybrid nanocomposite against steel were characterized comprehensively. A similar nanostructure was produced by high energy ball milling of the three identified tribofilm constituents: silica, hematite and graphite. By supplying powders to a pin-on-disc test it has been shown that neither silica, nor hematite, nor a mixture of both provide the low coefficient of friction (COF) observed for the hybrid composite. Only if graphite was blended with the oxides, the low COF was obtained. Thus, a film of finely dispersed stable inorganic wear products containing 15 vol% graphite provides low friction and wear in the considered case.
We applied a combination of Raman spectroscopy (RS) and cross-sectional transmission electron microscopy (X-TEM) to identify silicone oil residues and tribofilms at steel disc surfaces after tribological testing. Neither chemical cleaning nor mechanical removal of a 50 µm thick surface layer produced a surface without any silicone residue. Nevertheless, long-term tribological properties are not affected due to silicone degradation which has been proved by Raman spectroscopy. Excellent anti-wear and anti-friction properties of a nanocomposite at severe stressing conditions correlated with the formation of a silica-based tribofilm containing amorphous and graphite-like carbon nanoparticles. Since reliable carbon quantification by analytical TEM is difficult, RS is a useful complementary method for carbon identification at wear scars.
High performance polymer composites have been intensively investigated for tribological applications in air, but rarely in hydrogen environment. Author's previous benchmark of composites in liquid hydrogen (LH2) showed that graphite filled polymers have beneficial friction behaviour in this extreme condition. Therefore, further investigations have been undertaken in hydrogen environment. This paper presents first results obtained with polyimide composites filled with different types (natural, synthetic) and amounts of graphite in air, vacuum and hydrogen environments. A particular attention is taken to the influence of hydrogen on graphite as well as on the polymer matrix.
The influence of hydrogen environment on the friction and wear behavior of polyimide (PI) composites was investigated for two different PI-types (PI1 and PI2) filled with natural or synthetic graphite. Sliding tests were run against AISI 52100 steel and the worn surfaces as well as the transfer film were analyzed by means of SEM, EDX and Infrared Spectroscopy. Results indicate that the chemical structure of the polyimide has a major influence on the tribological behavior. While the friction of PI2 remains rather stable in all environments, PI1 showed very low friction in hydrogen without any lubricant. The lubricity of graphite was found to be more effective in hydrogen than in moist air.
Die tribologischen Eigenschaften von graphitgefüllten Polyimiden gegen Stahl 100Cr6 wurden an Luft, im Hochvakuum (l0⁻ ³ Pa) und in Wasserstoffumgebung bei verschiedenen Drücken (10³ Pa, 10⁴ Pa und 10⁵ Pa) untersucht. Zwei unterschiedliche Polyimid-Typen wurden eingesetzt, wobei Typ und Menge des Graphits variiert wurden.
Die Experimente wurden bei 3,1 MPa Kontaktdruck und einer Gleitgeschwindigkeit von 0,2 m/s bzw. 1 m/s durchgeführt. Die verschlissenen Oberflächen und die Morphologie des Materialübertrags auf die Stahl-Gegenfläche wurden mittels Lichtmikroskopie, REM, TEM und FTIR untersucht. Die Untersuchung zeigt, dass sowohl die Matrix als auch der Graphitanteil einen deutlichen Einfluss auf das Reibverhalten von Verbundwerkstoffen in Wasserstoffumgehungen haben können.