Improving mechanical performances at room and elevated temperatures of 3D printed polyether-ether-ketone composites by combining optimal short carbon fiber content and annealing treatment

Development of high performance polyether-ether-ketone (PEEK)) composites is of great significance for aerospace engineering application. The fused filament fabrication (FFF)-based 3D printing process is promising for manufacturing high performance short carbon fiber (SCF) reinforced PEEK composites. However, a comprehensive investigation of the combined effects of SCF content and annealing condition has not been conducted on the mechanical performances of SCF/PEEK composites; also, elevated temperature mechanical properties that are required for aerospace engineering have not been reported for 3D printed SCF/PEEK composites. This work develops a creative strategy that combines the optimal short carbon fiber (SCF) content with annealing treatment to achieve significant improvements in the mechanical properties both at room and elevated temperatures of FFF-3D printed SCF/PEEK composites. First, the influences of SCF content on the mechanical performances of 3D printed SCF/PEEK composites are studied to determine the optimal fiber content (5 wt%) for the best mechanical performances of non-annealed PEEK composites. Then, the effects of SCF content and annealing on room temperature and elevated temperature mechanical performances are examined for both PEEK and the 5 wt% SCF/PEEK composite. It is elucidated that the increase of interface strength and crystalline region as well as the reduction of residual stress by annealing are all responsible for the observed improvements in mechanical performances. This work presents a comprehensive study of 3D printed short fiber reinforced thermoplastics and serves as a valuable reference for the 3D printing of high-performance thermoplastic composites.