The wear and friction of polyamide 46 and polyamide 46/aramid-fibre composites in sliding–rolling contact

Polyamide 4,6 (PA46) and its aramid fibre composites (6 wt.%, 12 wt.% and 15 wt.%) were tested as candidate materials for tribological applications using a twin-disc wear test rig, built in our laboratories, to measure their wear and frictional properties under variations of number of cycles (103 to 106), applied load (300–600 N) and applied velocity (500, 1000 and 1500 rpm), all at a slip ratio of 2%. The rig uses polymer-on-polymer non-conformal contacts with varying proportions of rolling and sliding and has previously been shown to be a more controllable model experiment than utilising the complex geometry of gears. Over the range of tests, the average coefficient of friction results showed that the PA46 + 15% aramid fibres generally had the lowest values compared to the other types of samples; however they generally had the highest steady wear rates, especially at higher loads and velocities. Using a thermal imager to record the temperatures created during the tests it was found that there was always an initial rapid rise in temperature followed by a slow decrease or a plateau, which seemed to follow the friction test results, with temperatures of up to 200 °C being reached. Optical microscopy of the wear surfaces of the PA46 samples showed cracks occurring for low loads and velocities, while at higher loads and velocities melting occurred. The PA46 + aramid fibre samples failed by pitting and large cracks/fractures occurring at the relatively high loads and velocities used. However, they may be suitable for tribological applications under appropriate conditions.