Tribological behavior of unfilled and carbon fiber reinforced polyether ether ketone/polyether imide composites

The friction and wear of injection molded Poly(ether ether ketone) (PEEK) and Poly(ether imide) (PEI), PEEK/PEI blends with the weight compositions of 50/50 %, 70/30 %, and 85/15 %, with and without short carbon fibers were measured in a pin(52100 steel ball)-on-disk(polymer blend) configuration under dry friction. 50/50, 70/30, and 85/15 compositions were annealed to study the effect of crystallinity on wear test. The test variables were sliding speed and normal load.

The wear mechanism of pure PEEK matrix was plowing and as the weight percentage of PEI in the blend was increased the wear mechanism changed to the generation of small particles. The wear rates of the unfilled PEEK/PEI blends were found to be a function of not only the blend composition, but also of the normal load, sliding speed and crystallinity in complex manner. However, the coefficient of friction of the unfilled blends did not seem to significantly depend on those testing parameters. When no wear debris was produced, it was below 0.15 otherwise it was ranged from 0.2 to 0.3. The 30 weight % carbon fiber reinforced (CFR) PEEK did produced wear particles but 70/30 and 100 % PEI composites showed reduced wear rates compared to those of unfilled blends. The coefficients of friction of CFR did not seem to be changed from those of the untreated blends except for 100% PEI. Presence of the incubation time before wear particles were produced indicated that the predominant wear mechanism was fatigue. An increase in friction correlated with the generation of wear particles and the formation of a wear groove.