Solidification mechanism and performance of vacuum 3D printed carbon fiber reinforced polyether-ether-ketone composites for in-space additive manufacturing

3D printing of composites in space is one of the most promising technologies for on-orbit manufacturing of space components, and the key to implementing in-space 3D printing of composites is to address the challenges brought by space extreme environments, especially high vacuum environment (VAC), during the forming process. In this research, short carbon fiber reinforced polyether-ether-ketone composites (SCF/PEEK) were manufactured by material extrusion-based 3D printing at a VAC level of 100Pa environment. Compared to atmospheric environment (ATM), the average surface roughness of VAC samples increased from 23.78 μm to 60.89 μm, and the crystallinity of VAC H-0, H-90 and V-90 specimens is 19.4 %, 12.9 % and 5.7 % greater than that of ATM specimens respectively. However, the tensile properties of H-0 and H-90 VAC samples decreased, and only the V-90 sample improved, with the average tensile strength and modulus increasing from 5.93 MPa to 1.47 GPa to 23.3 MPa and 3.76 GPa, respectively. Based on three-dimensional heat transfer analysis, the solidification mechanism of VAC 3D printed SCF/PEEK was established to find out the reasons for the above phenomena. The low radiation heat dissipation efficiency of composite melt in VAC deduced its solidification speed, which was conducive to sufficient molecular orientation movement and interlayer diffusion entanglement, but also faced the issues of uncontrollable rheology and expansion of small air pores into large defects. These factors together determined the forming quality of 3D printed SCF/PEEK composites. This study points out the development direction for further optimizing the forming process of 3D printed PEEK composites, which could accelerate the technological progress for in-orbit construction of space structures.