Characteristics and mechanism in ultrasonic vibration-assisted deformation of Ni-based superalloy thin-walled sheet by quasi-in-situ EBSD

Ultrasonic vibration-assisted (UVA) forming is expected to be an effective way to improve the forming ability of Ni-based superalloy thin-walled sheet. However, the deformation characteristics and mechanism of this material under ultrasonic field keep unclear. To this end, experiments of UVA tension followed by quasi-in-situ EBSD were conducted. The tensile mechanical properties under different amplitudes were investigated, and the quasi-in-situ microstructure evolutions of the feature areas on non-UVA/UVA tensile specimens were compared. Experimental results show that ultrasonic vibration reduces the stress response, but the fracture may occur in advance under excessive ultrasonic amplitude. During the UVA deformation, the easy-to-deform grains with initial orientation close to<101>along the tensile direction rotate to<111>and<001>orientations, which then have a tendency to rotate back to<101>orientation in subsequent deformation. In addition, low-angle grain boundaries and dislocation density are also promoted. Based on the experimental results, a new perspective of the acoustic softening mechanism considering grain rotation and dislocation slip was proposed. The ultrasonic vibration facilitates grain rotation to coordinate plastic deformation. Meanwhile, the superposition of the ultrasonic field intensifies the atomic inherent vibration. The lattice resistance required for dislocation slip decreases accordingly.