Laser polishing of LPBF IN718 forms dislocation cells and enhances high temperature ductility

The high-temperature performance of current additively manufactured IN 718 alloy is critically limited by synergistic effects of surface-topography-induced stress concentrators, and subcritical porosity, particularly the thermal softening of the γ″ phase and its heterogeneous distribution within grains at 650 °C. Here, we propose a laser polishing treatment strategy that reconstructs both surface and sub-surface architecture of LPBF Inconel 718 alloy. This approach significantly reduces surface roughness from Ra ≥ 10 µm to Ra ≤ 1 µm, eliminates near-surface porosity by up to 65.7 %, and forms a refined, uniform nanometric dislocation cell. High-temperature tensile tests demonstrate plasticity performance nearly doubled at 650 °C with only 3 % yield strength loss. The detailed fractographic and microstructural analyses have confirmed that the enhanced plasticity originates from: (1) stabilized dislocation cell structures that homogenize stress distribution and suppress grain boundary cracking, (2) elimination of columnar grain morphology through dynamic recrystallization, and (3) delayed crack initiation and propagation between 550 and 650 ℃ due to dislocation cell structural confinement. Laser polishing produces a near-surface dislocation-cell structure engineering emerges as a transformative post-processing strategy, enabling additively manufactured IN718 alloy to overcome intrinsic high-temperature limitations through dislocation cell, thus redefining the strength-ductility paradigm at elevated temperatures.