Understanding the multi-scan strategies in L-PBFed CF/PEEK composites: micro–macro tests and multi-scale modelling

This study investigates the role of multi-scan strategies in expanding the processing window of laser powder bed fusion (L-PBF) for high-fibre-content carbon fibre reinforced polyetheretherketone (CF/PEEK) composites. Combining X-ray computed tomography (XCT) characterisation with mechanical testing demonstrates that multi-scan strategies effectively decrease porosity in high-fibre-content L-PBFed CF/PEEK composites. For composites with 20 wt% fibre content, progressive scan repetitions significantly improve densification, attaining near-full density after eight-pass scanning along with a tensile strength of 148 MPa. Additional scans similarly diminish porosity in 25 wt% fibre content composites, though the levels persistently exceed those of 20 wt% fibre content composites. To deeper investigate these mechanisms, a sequentially coupled discrete element method and computational fluid dynamics (DEM-CFD) framework is developed, integrating the high-fidelity multilayer DEM model for powder spreading dynamics with the multiphase melting pool model featuring bidirectional energy exchange. The model uncovers that 20 wt% composites accomplish thorough matrix fusion and fibre encapsulation, while 25 wt% composites still exhibit persistent structural discontinuities caused by matrix deficiency and fibre agglomeration, even with additional scanning passes. These findings push forward the processability limits of L-PBFed polymer composites, establishing a strategic framework to achieve improved mechanical performance through optimised scanning protocols.