Влияние структуры матрицы на трибологические характеристики твердосмазочных композитов на основе высокотемпературных термопластов полиимида

Abstract

The structure, mechanical and tribological properties of polyimide (PI) and polyetherimide (PEI) based composites, which differ by the presence of "hinged" oxygen atoms in the polymer’s molecular chain have been studied. The composites were reinforced with chopped carbon fibers and simultaneously loaded with organic (PTFE) and inorganic (MoS2) solid lubricant fillers. Tribological tests were carried out according to the «ball-on-disk» scheme under dry sliding friction on a ceramic counterface in the temperature range of T = 23-180 °C. It has been shown that only the «PEI/10% CF/10% PTFE» composite possesses the highest wear resistance in the entire temperature range studied. At the same time, the loading with PTFE particles ensured the formation and adhering of a stable layer of secondary structures (transfer film layer) on the sliding surface of the polymer composite. Changes in wear intensity and friction coefficient correlated well with each other. When the MoS2 solid lubricant filler were loaded, the transfer film was fixed on the sliding surface of the composite only at the highest testing temperature T = 180 °C. This was ensured by the presence of oxygen atoms in the PEI molecules. In so doing, formation of the transfer film layer gave rise to low coefficient of friction and relatively high wear resistance of the «PEI/10 CF/10 MoS2» ternary composite. A comparative analysis of the tribological properties of two types of polymer matrices have shown that the wear rate of PEI based composites loaded with PTFE was identically low at T = 23°C and 120°C, while at T = 180°C it was 300 times lower in contrast to PI-based ones. We suggest that this was related to the more «rigid» nature of the PI matrix (which does not contain «hinged» units in the macromolecule). Under conditions of a high and oscillating friction coefficient, the PI matrix was not capable of adhering a solid lubricant PTFE-containing transfer films layer. The PEI-based composites are recommended for use in tribounits due to both high manufacturability (processability) governed by the flexibility of the polymer chain, and high wear resistance due to the formation of stable secondary structures on sliding surfaces in the temperature range T = 23-180 °C.