Crack suppression in additively manufactured non-weldable γ′ Ni-based superalloys by tailoring the melt-pool flank shape

To address solidification cracking in non-weldable γ′-strengthened Ni-based superalloys fabricated by powder bed fusion-laser beam (PBF-LB), this study achieves crack suppression through tailoring the melt-pool flank shape. Using Mar-M247 alloy as a representative, nearly crack-free PBF-LB specimens were successfully fabricated. Compared to conventionally additively manufactured Mar-M247 alloys, the optimized specimens show a 31.6% (from 1075 MPa to 1414.7 MPa) increase in strength and a 200% (from 5.4% to 16.2%) improvement in elongation. A moderate reduction in linear energy input (LED) increased the melt-pool width-to-depth ratio and produced a shallower melt pool with less steep melt-pool flanks, thereby aligning the local thermal-gradient direction more closely with the build direction (BD). This promoted columnar grains with < 001 > orientations nearly parallel to the BD, reduced inter-columnar misorientation, and suppressed crack initiation and propagation. Meanwhile, refined grains near the melt-pool flanks further alleviated local strain concentration and contributed to crack inhibition. In addition, the higher solidification rate restricted solute diffusion and promoted Hf trapping in the γ matrix, narrowing the solidification temperature range and decreasing crack susceptibility. Serrated grain boundaries further increased resistance to intergranular crack propagation. This work provides guidance for suppressing cracking in PBF-LB non-weldable γ′-strengthened Ni-based superalloys.