Abstract: Additive manufacturing (AM) Ni-based superalloys face challenges in generating high-density annealing twins via conventional heat treatment (CHT) methods. In this study, an innovative electropulsing treatment (EPT) was proposed as a post-processing strategy for 718Plus alloy fabricated by laser-directed energy deposition (LDED). The results revealed that EPT rapidly eliminated the Laves phase, reduced residual stress, and refined grains by 65 % (from 164.8 to 57.2 µm), forming high-density annealing twins (56.5 % twin boundary fraction). Compared with as-deposited (AD) samples, EPT samples had a remarkable improvement in plasticity. The elongation increased significantly from 3.5 % to 59.5 %, while maintaining high ultimate tensile strength (949 MPa), transitioning from brittle to ductile fracture. EPT reduced the recrystallization thermodynamic barrier, enhanced the atomic diffusion flux, and effectively promoted the recrystallization process. The formation of high-density annealing twins was attributed to enhanced grain boundary mobility and reduced matrix stacking fault energy (SFE) through EPT. During plastic deformation, twin boundaries (TBs) played a crucial role in enhancing the plastic deformation of the alloy. They coordinated intergranular plastic deformation, activated the multi-slip system, and interacted synergistically with stacking faults (SFs), deformed twins, and the Lomer-Cottrell (L-C) locks. This study provides a new strategy for efficient post-processing and strength-ductility synergistic optimization of AM Ni-based superalloys.

Key words: 718Plus alloy, Additive manufacturing, Electropulsing treatment, Annealing twins, Tensile properties