Evolution of microstructure and thermo-mechanical attributes of fiber reinforced polyamide during fused deposition modeling 3D printing: A comprehensive characterization study

Fused deposition modeling (FDM), a type of additive manufacturing is widely used for complex mold design, single-part tool manufacturing, and prototyping. The FDM process, especially with fiber-reinforced filament, induces intricate changes that influence microstructure and properties, highlighting the necessity for a thorough understanding to maximize FDM utilization. This study comprehensively examines microstructural changes and mechanical attributes in polyamide (PA) and carbon fiber-reinforced polyamide (CF-PA) before and after FDM printing. Through various characterization techniques including X-ray diffraction, thermal gravimetric, differential scanning calorimetry, tensile testing, micro-Computed Tomography (mu-CT), and fractography, insightful perspectives were obtained. Results reveal substantial fiber breakage, resulting in a 33.03% decrease in the average fiber length from filament to printed parts. X-ray mu-CT scans illustrated a more pronounced fiber alignment in CF-PA filament than in the CF-PA printed sample. TG analysis confirms approximately 20 wt.% CF content in the filament, with negligible residue in pure PA filament and samples. DSC shows enhanced thermal stability with CF reinforcement, while XRD confirms amorphous behavior in filament and printed parts. Tensile tests reveal anisotropic properties in FDM samples. The addition of short CFs increases Young's modulus but decreases strength. Examination of fractured surfaces reveals different failure modes for filament and printed coupons.