Improvement of Heat Treatment Process on Mechanical Properties of FDM 3D-Printed Short- and Continuous-Fiber-Reinforced PEEK Composites

Due to the addition of short/continuous fibers with better mechanical properties, FDM 3D-printed short- and continuous-fiber-reinforced PEEK composites possess better performance than printed PEEK. However, the interlayer bonding performance becomes poor due to the layer stacking and weak fiber–resin interface adhesion. In this study, a heat treatment process was proposed to improve the interlaminar bonding properties of 3D-printed short- and continuous-fiber-reinforced PEEK composites. The effects of heat treatment temperature and time on the interlaminar shear strength, porosity and dimensional change of printed samples were studied by a single-factor experiment. Moreover, the thermal properties and fracture morphology of FDM 3D-printed fiber-reinforced PEEK composites before and after heat treatment were investigated to explore the toughening and strengthening mechanism. The experimental results showed that the mechanical properties of FDM 3D-printed fiber-reinforced PEEK composites improved by heat treatment process can be attributed to the improvement of crystallinity and interfacial bonding. The heat treatment process can also improve the infiltration and diffusion among adjacent filaments and layers, and further reduce the defects. The optimized heat treatment temperature and time were 250 °C and 6 h, respectively. The maximum ILSS of FDM 3D-printed short- and continuous-fiber-reinforced PEEK composites increased by 16 and 85% compared with untreated samples, respectively.