2026-10-07T16:37:36Z https://www.scidb.cn/oai

10.57760/sciencedb.0139i 2026-09-28T09:50:49Z

2026-09-28 Granularization of the elongated rod-like δ phase and the strengthening mechanism arising from the synergy between granular δ phase and the thermo-mechanical coupling effect during friction stir processing of WAAM IN718 alloy doi:10.57760/sciencedb.0139i en The granular δ phase can improve the mechanical properties of wire-arc additively manufactured Inconel 718 (WAAM IN718) alloy. However, conventional heat treatments struggle to simultaneously optimize the granular morphology and the volume fraction of the δ phase. In this study, a δ-phase precipitation heat treatment (HT) was employed to maximize the volume fraction of the δ phase without compromising the subsequent precipitation of γ' and γ''. The feasibility of using friction stir processing (FSP) to fragment the elongated rod-like δ phase into granular δ phase was then explored. By combining characterization techniques including high-resolution transmission electron microscopy, scanning electron microscopy, electron backscatter diffraction, and X-ray diffraction, the synergistic role of the fragmented granular δ phase and the thermo-mechanical coupling effect during FSP in optimizing the microstructure was revealed. The characterization results show that in the stir zone of the HT - FSP processed WAAM IN718 alloy, the Laves phase, δ phase, γ' and γ'' were completely dissolved, whereas in the interface transition zone γ' and γ'' were dissolved but the Laves phase and δ phase were retained and fragmented into a granular morphology, distributing uniformly in the γ matrix. After a second double-aging treatment, γ' and γ'' re-precipitated in the stir zone, and the corresponding tensile properties were significantly improved. Compared with the as-built state, the elongation decreased by only 30.3%, while the ultimate tensile strength and yield strength increased by 119.6% and 261.8%, respectively. In addition, during FSP cooling, the granular δ phase pinned dislocations and hindered grain boundary migration, which suppressed growth of recrystallized grains and induced the formation of serrated grain boundaries with a higher dislocation storage capacity. Consequently, the hardness and strength of the interface transition zone, which contained abundant granular δ phase, were both significantly higher than those of the stir zone. This study confirms the feasibility of using FSP to actively fragment the elongated rod-like δ phase and verifies the synergistic effect between the granular δ phase and the thermo-mechanical coupling effect during FSP in improving the microstructure and properties of the alloy. It therefore lays the foundation for the subsequent introduction of a specific cooling process to prevent the dissolution of the granular δ phase in the stir zone, thereby comprehensively enhancing the mechanical properties of FSP joints, and provides new insights for the design of post-processing routes for WAAM IN718 alloy. Friction stir processing; Room-temperature tensile properties; Wire arc additive manufacturing; Inconel 718 Zhiquan Zhou Tao Yuan Zhenghao Liu Yixiang Wang Junyu Song He Shan Shujun Chen PUBLIC https://creativecommons.org/licenses/by/4.0/ dataset Science Data Bank