Many inherent issues, such as the detrimental residual stress, columnar grains with anisotropy, and weak mechanical properties, have severely impeded the adoption of metal additive manufacturing (AM) techniques including powder bed fusion and directed energy deposition (DED) processes. In this study, a hybrid AM process that consists of layer-wise laser metal deposition (i.e., a DED process) and in-situ ultrasonic impact peening (UIP) was applied to obtain Inconel 718 superalloy workpieces. Also, for further property enhancement, a post-heat treatment was applied to the deposited material obtained by the hybrid AM process. Scanning electron microscopy and transmission electron microscope were used to investigate the microstructure morphology and reveal the underlying strengthening mechanism. Electron backscatter diffraction was employed to quantitatively study the microstructure resulted from the hybrid AM process and the post-heat treatment. The profile of residual stress along the depth direction was obtained through X-ray diffraction. The results demonstrate that this hybrid AM process is capable of producing high-quality metal parts with significantly refined microstructure, and beneficial compressive residual stress along the depth into surface. Severe plastic strains are introduced by UIP, and the resulted mechanical twinning and dynamic recrystallization play an important role in refining microstructure. The material microstructure is further refined down to 100 µm, and the texture anisotropy is significantly diminished after solution treatment at 980 °C for 1 hour. Under the as-built condition, in-situ ultrasonic peening alters the residual stress component from a tensile state to an overall compressive state with a maximum value of − 190 MPa within the range of measurement depth.

中文翻译：

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原位超声冲击强化定向能量沉积法制备 Inconel 718 的显微结构和性能

许多固有问题，例如有害的残余应力、具有各向异性的柱状晶粒和弱的机械性能，严重阻碍了金属增材制造 (AM) 技术的采用，包括粉末床熔融和定向能量沉积 (DED) 工艺。在这项研究中，应用由分层激光金属沉积（即 DED 工艺）和原位超声冲击强化 (UIP) 组成的混合 AM 工艺来获得 Inconel 718 高温合金工件。此外，为了进一步提高性能，对混合 AM 工艺获得的沉积材料进行了后热处理。使用扫描电子显微镜和透射电子显微镜研究微观结构形貌并揭示潜在的强化机制。采用电子背散射衍射对混合增材制造工艺和后热处理产生的微观结构进行定量研究。通过X射线衍射获得沿深度方向的残余应力分布。结果表明，这种混合 AM 工艺能够生产出具有显着改善的微观结构和有益的沿表面深度的残余压应力的高质量金属零件。UIP 引入了严重的塑性应变，由此产生的机械孪晶和动态再结晶在细化微观结构中起着重要作用。材料微观结构进一步细化至100μm，在980°C固溶处理1小时后，织构各向异性显着减弱。在建成条件下，