Unveiling crack mitigation pathways in powder bed fusion–laser beam of CM247LC: an operando X-ray radiography study of Hf and nano-Y₂O₃ additions

Cracking presents a major hurdle for processing non-weldable Ni-base superalloys, such as CM247LC, by powder bed fusion–laser beam (PBF–LB). This study directly observes cracking behavior in standard CM247LC and two admixed alloys (CM247LC + 1 wt.% Hf and CM247LC + 1 wt.% nano-Y₂O₃) using operando synchrotron X-ray radiography synchronized with acoustic emission (AE). Our real-time data confirm extensive cracking in the standard alloy is identified to be primarily solidification cracking. Both Y₂O₃ and Hf additions mitigate solidification cracking, though through distinct mechanisms. Nano-Y₂O₃ addition alters the processing regime from keyhole to conduction mode. Scheil solidification simulations predict a narrower solidification range and lower solidification cracking index (SCI). This indicates that a combination of processing regime shift along with modification in solidification as the primary drivers for crack suppression upon addition of nano-Y₂O₃, despite increased lack of fusion and complex oxide formation. Hf-addition mitigated cracking via enhanced segregation at interdendritic regions, promoting beneficial carbides and improved liquid backfilling. Scheil simulations for alloy with Hf-addition predicted low SCI compared to standard CM247LC due to increased liquid availability in final solidification stages. These insights highlight that nearly crack-free PBF–LB of non-weldable superalloys can be achieved through both the powder modifications.