Ultrasonic rolling-enhanced additive manufacturing of IN718 superalloy: Microstructural refinement and mechanical property improvement through variable power modulation

Conventional wire and arc direct energy deposition (WADED) of nickel-based superalloys faces critical challenges, such as, coarse columnar grains, pronounced elemental segregation, and suboptimal mechanical performance, hindering their applications in high-value aerospace industries. Herein, we developed an ultrasonic rolling-assisted WADED (UR-WADED) strategy that synergistically couples dynamic plastic deformation with in-situ ultrasonic vibration. Through systematic modulation of ultrasonic power (0–90 %), its effects on dendritic evolution, phase transformation, and dislocation dynamics were decoupled. Multiscale characterization revealed that ultrasonic mechanical excitation induced three key effects: (1) grain refinement was achieved through the combined effects of acoustic cavitation and rolling. Under high-power UR, a mixed grain structure was formed, and the average grain size in the fine-grained region was reduced by 80.5 % (from 178.68 μm to 34.87 μm); (2) The joint action of acoustic streaming and rolling transformed the morphology of the Laves phase from a continuous chain-like distribution into a more dispersed island-like form; (3) Texture randomization occurred, with the maximum intensity of the (001) pole figure reduced by 62 %, accompanied by the generation of a high density of intragranular dislocations. The optimized 90UR-WADED specimen exhibited significant property enhancement: Vickers hardness increased by 42.5 % (376.2 vs 264.1 HV_0.5), while yield and ultimate tensile strengths surged to 768.2 (+55.5 %) and 1072.9 MPa (+38.9 %), respectively, outperforming conventional WADED counterparts. Quantitative strengthening analysis identified grain boundary strengthening (∼59 %) and dislocation hardening (∼23 %) as dominant mechanisms. After heat treatment, the 90UR-WADED sample exhibited a fully equiaxed grain structure, and its mechanical properties surpassed those of wrought IN718. This work established a notable hybrid manufacturing approach that overcomes the intrinsic limitations of arc-based additive manufacturing and provides a scalable pathway for fabricating high-performance superalloy components.