Dispersoid coarsening and slag formation during melt-based additive manufacturing of MA754

We have assessed the structural evolution and dispersoid coarsening behaviors of the oxide dispersionstrengthened superalloy MA754 during two different melt-based additive manufacturing techniques - metal laser powder bed fusion (PBF-LB/M) and directed energy deposition (DED). The mechanically alloyed MA754 powder posed challenges for both processes due to its irregular flaky morphology and large particle size. Successful consolidation with PBF-LB/M required increasing the layer height, decreasing the scanning speed, and increasing the laser power relative to typical Ni superalloy printing parameters. The resulting materials contained residual porosity and large Y-Al-oxide slag inclusions which formed in situ. The more prolonged thermal excursion during DED resulted in even larger, mm-scale slag inclusions, which spanned several build layers. In both PBF-LB/M and DED, these inclusions grew at the expense of nanoscale dispersoids, depleting the material of this strengthening phase. These observations motivate alternative approaches for preparing dispersionstrengthened powder feedstocks besides mechanical alloying and highlight the deleterious effects of Al microalloying on dispersoid stability and structure.