Friction and Wear of Polyimide and Graphite Filled Polyimide Composites under Hydrogen Environment

It is important to understand tribological characteristics of components operating in a hydrogen atmosphere. For instance, piston rings used in reciprocating compressors require strength, heat resistance and wear resistance, hence resins containing fillers are used. Particularly at high-pressure stages, PEEK- or polyimide (PI)-type composite resins are often introduced. In this study, focusing on PI and its composites, we investigated sliding properties of the resin in the hydrogen environment and the structure of transfer film. It was confirmed that some PI without fillers had good sliding properties and this unfilled PI exhibited sliding properties which was equivalent to other graphite-filled PI. A cross-sectional TEM EELS analysis revealed that the transfer film was a layer mainly composed of carbon. Raman analysis suggested that, in case of unfilled PI, the transfer film of carbon was formed by the decomposition of the PI due to wear, whereas in case of graphite-rich PI resin, the film was created mainly by decomposition of graphite. These results suggest that the carbon layer of the transfer film, which comes from sliding in the hydrogen environment, improves friction and wear properties, indicating that the origin of the layer may be irrespective of whatever it is (e.g., PI, graphite, etc.).