From micro- to macro-cracks and recrystallization in a non-weldable Ni-based superalloy manufactured by electron beam powder bed fusion

In the present study, CM247LC, a non-weldable Ni-base superalloy, was fabricated by electron beam powder bed fusion (EB-PBF) over a wide energy levels. For this purpose, variable process parameters were adjusted to investigate their effect on microstructure and crack formation. Samples fabricated at both low and high area energies exhibited pronounced crack susceptibility. At very low energy densities, lack of fusion (LoF) and porosities were observed, while higher energy densities produced denser samples. Adjustments to energy density and process parameters resulted in a grain structure transition from fine-columnar to coarse-columnar and near-single crystal morphologies. Despite these changes, the cracking issue persisted, with micro-cracks observed in low-energy samples and macro-scale cracks, several millimeters long, forming at higher energy densities, highlighting the material’s high sensitivity to crack formation. Both solidification and liquation cracking were identified— the former showing dendritic crack surfaces, and the latter associated with eutectic phases and grain boundary precipitates. Severe recrystallization around cracks was observed at high energy densities, characterized by elevated dislocation densities. EDS analysis revealed hafnium- and silicon-rich precipitates in interdendritic regions and near cracks, contributing to severe hot cracking in the material.