Effect of serrated grain boundaries on tensile properties of laser powder bed fusion fabricated Inconel 718

This study elucidates the coupled effects of grain boundary architecture and precipitation strengthening on laser powder bed fusion (L-PBF) Inconel 718. Through graded solution treatments, three grain boundary morphologies were engineered: straight (S1) and serrated (S2/S3) with controlled δ-phase distribution. Serrated grain boundaries (SGBs) enabled strength-ductility synergy, preserving yield strength (1150–1168 MPa) while increasing elongation by 10.8–23.2 % compared to straight boundaries. SGBs geometrically suppressed crack initiation and reduced propagation rates via crack path deflection. Cyclic testing revealed SGBs redistributed dislocation storage, lowering geometrically necessary dislocation density by 14.3 % and back stress dominance. Strain hardening analysis revealed that SGBs maintained a dynamic equilibrium between back stress (603 MPa) and friction stress (328 MPa), thereby delaying the onset of strain localization through coordinated stress redistribution. Precipitation analysis identified γ″ (20.8–21.4 nm) as the dominant strengtheners via coherency (51–54 %) and ordering (85–86 %) effects. Numerical modeling achieved optimal mechanism superposition (k = 1.2–1.3) between theory and experiment. These findings establish microstructure-property linkages for additive superalloys, demonstrating SGB-δ-phase synergy enables damage-tolerant design for extreme environments.