Solidification and Crack Defect Formation on the Single Melt Track Scale for High γ^′ CoNi-Base Superalloy Variants

Additive manufacturingAdditive manufacturing enables the fabrication of complex part geometries, and is attractive for advanced aerospace components. Laser powder bed fusion (LPBF)Laser Powder Bed Fusion (LPBF), specifically, is being assessed for manufacturing structural components of gas-turbine engines made from high-γ^′ volume fraction superalloys. However, the formation of crack defects during LPBFLaser Powder Bed Fusion (LPBF) of nearly all superalloys within this class has undercut their mechanical performance greatly. This study builds on prior work examining the cracking susceptibility of high-γ^′ volume fraction superalloys during LPBF by simplifying the LPBF process down to single track laser meltingLaser melting scans. The CoNi-base alloy GammaPrint-700 is utilized in this study, as the cracking resistance of the alloy can be controlled through the boronBoron content. A means of improving the cracking resistance of the alloy through homogenization treatments prior to laser meltingLaser melting was identified. Characterization of the single tracks reveals a possible mechanism of crack initiationCrack initiation via liquation cracking of grain boundariesGrain boundary in the substrate material, and propagation via solidification crackingSolidification cracking along grain boundariesGrain boundary in the melt pool. Additionally, a protocol for assessing the cracking resistance while developing new high-γ^′ volume fraction superalloys for additive manufacturingAdditive manufacturing is discussed.