Comparison of microstructure, mechanical properties, and strengthening mechanisms of PBF-LB/M fabricated with PM high γ′ Ni-based superalloys

Additively manufactured high-γ′ superalloys often require hot isostatic pressing (HIP) and heat treatment (HT) to eliminate cracks. However, their microstructural homogeneity is still inferior to that of traditional powder metallurgy (PM) or wrought superalloys, and the impact on the alloy's mechanical properties is not yet clear. Therefore, this study systematically investigates the influence of microstructural differences among metal powder bed fusion-laser beam (PBF-LB/M), PBF-LB/M+HIP, PBF-LB/M+HIP+HT, and PM alloys on their tensile properties and deformation mechanisms. Optimized PBF-LB/M parameters yield a relative density of 99.6%. The as-printed alloy exhibits coarse columnar grains (57.5 μm), a high dislocation density cellular substructure, and elemental segregation. Post-processing (HIP+HT) promotes grain refinement (34.8 μm) and the formation of uniformly distributed nano-scale γ′ precipitates (96.6 ± 8.5 nm). Compared to the PM alloy (grain size 16.4 μm), the PBF-LB/M+HIP+HT alloy exhibits coarser grains, residual chemical inhomogeneity and localized strain. Consequently, its room-temperature ultimate tensile strength (1591.4 MPa) and elongation (24.1%) are slightly lower than those of the PM alloy (1617.4 MPa/26.8%). Deformation in the PBF-LB/M+HIP+HT alloy is dominated by planar slip, whereas the PM alloy exhibits multiple slip bands. At 750°C, both alloys exhibit highly consistent performance, as deformation is governed by γ′ precipitation strengthening via stacking fault/twinning shearing accompanied by 9 R phase formation, synergistically enhancing strength and toughness. This work demonstrates that optimized PBF-LB/M+HIP+HT processes can achieve high temperature performance comparable to PM, providing theoretical support for the application of additively manufactured components.