Reducing porosity and tailoring material properties in dual-laser additive manufacturing via scanning trajectory optimization

While multi-laser additive manufacturing has revolutionized the throughput of large-scale component fabrication, universal protocols for spatially tailoring material properties remain elusive. Currently, as-printed parts are constrained to uniform performance, and their potential for site-specific microstructural control has not been fully exploited. Here, we report a scanning trajectory orchestration strategy that could transcend this limitation, enabling both the suppression of defects in the laser overlapping region and the customization of mechanical performance. Scanning paths parallel to the laser overlapping regions can effectively suppress defect formation. Furthermore, we demonstrated that modulating local thermal histories enables on-demand tailoring of Ti-6Al-4V mechanical properties in three dimensions, achieving a modulation range of over 25% in ultimate tensile strength or over 100% for ductility. Microstructural differences resulting from the varied thermal histories of different scanning paths form the foundation for property tuning. Notably, the key to realizing performance control in the inter-layer is ensuring that the same trajectory print height exceeds the affected zone height. This scanning trajectory orchestration strategy was also validated across three distinct alloy systems without feedstock modification or post-heat treatment. Our work provides both theoretical and experimental foundations for tailoring the mechanical properties of monolithic components via scanning trajectory programming. This capability paves the way for manufacturing functionally graded properties, which are crucial for next-generation aerospace and automotive applications.