Tribological behavior evaluation of poly-ether-ether-ketone (PEEK) in dry journal bearing on shaft wear test

This paper investigated the tribological behavior of pure PEEK playing as a dry journal bearing, sliding against stainless steel, under real-life operating conditions in a wear test lasting 2 h. Four conditions were carried out with different magnitudes of normal load and sliding speed, while keeping a constant PV parameter. Sample topography assessments were performed with scanning electron microscopy and white light interferometry techniques. In addition, PEEK samples were also evaluated by Fourier Transformed Infrared Spectroscopy and thermal analyses by Differential Scanning Calorimetry. The coefficient of friction (COF) changed throughout the wear test and exhibited a running-in period followed by a transition, with an increase of COF, and then a tendency to reach a steady-state. Moreover, the COF behavior obtained suggests that there was an influence of the wear test parameters, mainly right after the running-in period - and the COF averages for the steady-state period were statistically equal. Stainless steel samples showed mild wear, while PEEK samples had a drastic alteration of their topography imposed by the wear test - including an increase in its degree of crystallinity. Nonetheless, the PEEK journal bearing samples did not fail from wear and their mass losses were small. Polymeric wear particles were generated and were found weakly adhered to both the body and the counter body. PEEK exhibited a lumpy transfer process - nonetheless, SEM images evaluation was useful to verify that these particles were eventually merged during sliding, and kneaded in the convex-concave contact, which provided them a film-like appearance. Furthermore, adhesive and abrasive wear mechanisms were identified, which were shown to be related to the journal bearing on shaft wear test arrangement.