Tribological anisotropy of PEEK composites filled with highly oriented carbon fibers manufactured by fused deposition modeling

The orientation of fibers in polymer matrix plays a crucial role in governing the performance of composites including friction and wear. In the present work, the effect of fiber orientation on tribological behavior of 3D printed short carbon fiber reinforced PEEK composites (CF/PEEK) was studied by two series of tribo-tests, namely macro-scale continuous sliding and micro-scale multiple scratching. Fiber orientations studied included parallel, tilted and anti-parallel relative to the sliding direction in both macro sliding and micro scratching. It was revealed that the effect of fiber orientation showed strong dependence on applied loads. In most cases, lower wear were obtained when the fiber orientation was tilted rather than parallel or anti-parallel in macro continuous sliding. With tilted orientation, the composite also exhibited the best scratching behavior except for that at the lowest normal load. To reveal the mechanisms behind this orientation effects, the composite's worn surface, as well as those of the counter rings, were characterized. Findings of the present work indicates that scratching tests can help understand the macro sliding mechanisms and appropriate fiber orientation is beneficial in improving the tribological properties of polymer composites, which can be realized through 3D printing.