Microstructure and defects in a Ni-Cr-Al-Ti γ/γ’ model superalloy processed by laser powder bed fusion

Additive manufacturing (AM) of non-weldable high-γ’ Ni base superalloys is challenging due to various issues, but notably because their inherent cracking propensity. Typically, the segregation melting point-depressant elements grain boundaries (GB) drastically increases solidification interval, allowing high processing-induced stresses in parts pull apart liquid film at GBs. To achieve a better understanding consolidation process nickel as well origin defects and cracks, simplified model γ/γ’-strengthened Ni-Cr-Al-Ti alloy with reduced related commercial CM247LC alloy, investigated under large parameter survey. The behavior typical produced by AM, optimal condition being compromise between porosity. mechanism is, however, changed solid-state cracking, localized high-angle GBs, likely lack GB strengthening phases inherently low strength this alloy. Transmission electron microscopy atom probe tomography reveal elemental Ti, lower extent Cr Al, cell boundaries, agreement Calphad calculations. No γ’ precipitates are observed as-processed condition, indicating that all remain solid solution. chemical differences cracked non-cracked boundaries. Trace amounts oxygen contained powder lead Al2O3 slag formation, nano oxide dispersoid incorporation. Sulfur, critical contaminant superalloys, detected rendered harmless formation TiS nanoprecipitates.