"Welding" the un-weldable: insights into PBF-LB processing of CM247LC

Additive manufacturing (AM) of the non-weldable Ni-base superalloy CM247LC via powder bed fusion – laser beam (PBF-LB) is challenging due to the solidification cracking during PBF-LB processing and strain age cracking (SAC) during post-processing heat treatment. Solidification cracking stems from thermal stresses during melt pool solidification, while SAC is driven by γ′ precipitation coupled with residual stresses from the PBF-LB process. This study employed multi-faceted approaches to mitigate these issues. Initial optimization of laser parameters (power, speed, hatch spacing) showed that low line energy density (<0.2 J/mm) and strong melt pool overlap (50–80%) reduced solidification cracking by promoting shallower melt pools. While lower volumetric energy density (VED) correlates with lower residual stresses, potentially alleviating SAC, it also increases lack-of-fusion porosity, necessitating alternative solutions for SAC. Electron Backscatter Diffraction (EBSD) identified that textured columnar grains reduce high-angle grain boundaries susceptible to solidification cracking. Novel scan strategies were then explored. Reducing laser stripe width from 5 mm to 0.2 mm significantly lowered crack density by promoting texture and reducing residual stresses by 30%. A demonstrator component with 0.2 mm stripes successfully underwent post-build heat treatment without SAC, unlike components with conventional 5 mm stripes. In-situ remelting strategies also showed promise in minimizing solidification cracking but complex behavior of residual stresses. Ongoing work investigates advanced scan strategies, such as laser beam shaping, for enhanced microstructure control to suppress both cracking forms. Results emphasize that processing CM247LC requires tailored approaches, distinct from weldable alloys, with grain structure and texture being crucial for defect mitigation. These insights offer a framework for advancing AM of crack-prone superalloys by balancing parameter optimization, scan strategy innovation, and microstructural engineering to produce robust, high-performance components.