Adhesive Wear Phenomena in High Performance Polyaryletherketones (PAEK) Polymers

Adhesive wear is one of the most difficult types to study and is especially challenging for polymers. Such wear processes involve the mutual sticking of surface asperities followed by removal of debris from the bulk. This differs from abrasive wear in which debris is formed due to the penetration of hard rough asperities into the softer surface. Such descriptions have served the polymer tribology community for decades and are well suited for post-mortem analysis of wear surfaces. For instance, the presence of rippled features on the wear surface and large flake shaped debris are typical indicators of adhesive wear. However, this approach offers little insight into the underlying physics that occur at the interface. The overall objective of this research is to gain fundamental knowledge of adhesive wear phenomena in polyaryletherketone (PAEK) polymers. Ultimately, the hope is to correlate the observed surface damage and friction response with material science based explanations. Since no true adhesive wear test configuration exists, a top down approach was used in designing a set of experimental conditions. This was done with a multi-axis tribometer capable of being programmed to a wide array of displacements and trajectories. A catastrophic form of adhesive wear is termed fretting and results from the repeated slip of mutually loaded contacts. Using the multi axis tribometer PAEK polymers were studied in both multi directional sliding and fretting configurations with varied environmental conditions. An important aspect of PEEK tribology is the surface temperature reached during sliding. Infrared thermography was used to observe the full field temperature map of PEEK during ball-on-disc sliding. Additionally, friction studies were performed with steel and sapphire counterfaces. The results of this study illustrate the important role transfer films play in determining both the friction and temperature response of the PEEK wear interface. The formation of transfer films resembles a unidirectional drawing process. Polarized FTIR-ATR measurements were used to assess chain orientation in the friction formed PEEK on steel transfer films. The results of these studies serve to better elucidate underlying mechanisms involved in adhesive wear of PAEK polymers