Effects of Extrusion Rate and Post-Annealing on Mechanical Properties and Printing Quality of Additively Manufactured Carbon Fiber Reinforced Polyetherketoneketone (PEEK) Parts

The development of high-temperature fused filament fabrication (FFF) 3D printers has enabled the additive manufacturing (AM) of polymers and composites with relatively high thermomechanical properties. Among them is polyetherketoneketone (PEKK) reinforced with short carbon fibers (CF-PEKK). PEKK is a high-performance thermoplastic that belongs to the polyaryletherketone (PAEK) polymer family with excellent mechanical properties. In particular, it offers a glass transition temperature of ~140°C, a relatively high modulus that can be readily enhanced by carbon fiber addition, and specific strength comparable to aluminum alloys. Therefore, there is a growing interest in using CF-PEKK to replace metal parts. Low dimensional accuracy and resolution, high porosity, and poor inter-layer strength [1-3] have limited FFF parts to rapid prototyping and non-structural applications. This paper aims to investigate extrusion rate, a printing parameter, and post-annealing as a potential solution to reducing porosity and enhancing inter-layer strength in CF-PEKK printed parts. A 5% increase in the theoretical extrusion multiplier (EM) resulted in a 1.6% reduction of void content accompanied by a 30% improvement in the inter-layer tensile strength of CFPEKK coupons. The impacts of extrusion rate and post-annealing (in a salt-packed container) on the printing quality of CF-PEKK parts are also determined. No significant structural or dimensional changes were detected with the higher extrusion rate or annealing in salt. This paper provides a new understanding of mechanical properties, processing, printability of CF-PEKK, and their AM challenges.