Investigation of acoustic softening and microstructure evolution characteristics of Ti3Al intermetallics undergoing ultrasonic vibration-assisted tension

[Display omitted] •Based on the wave equation and the resonance theory of non-uniform material, a uniaxial tension device with ultrasonic vibration assistance for Ti3Al intermetallic compounds was designed.•The acoustic residual hardening induced by a small amplitude was dominant, while a large amplitude led to acoustic softening.•As ultrasonic vibration was applied, the fracture mode of Ti3Al evolved from the ductility dimple fracture to the mixed mode of cleavage pattern and brittle fracture.•The “defective phase” structure in the α2 phase and B2 matrix was discovered and it extended from the vicinities of the fracture cross-section to the area away from the fracture cross-section as vibration amplitude was enlarged. Ultrasonic vibration-assisted deformation (UVAD) technology has been widely utilized in the metallic materials forming and manufacturing process owing to its advantages of effectively reducing deformation stress. However, the intrinsic mechanism of UVAD involved in Ti3Al intermetallics has not yet been clarified. In this research, an ultrasonic vibration tension device for Ti3Al was designed. The mechanical properties under ultrasonic vibration-assisted tension (UVAT) were investigated. Subsequently, the rheological behavior under the effect of ultrasound was analyzed. The influences of the vibration amplitudes and vibration modes on the microhardness and microstructure were explored. The results indicated that Ti3Al behaved obviously an acoustic softening after introducing ultrasonic energy, and the degree of softening was positively correlated with amplitude. There was a “competitive” relationship between the acoustic softening and acoustic residual hardening effects. The maximum stress and microhardness reductions were 206.13 MPa and 6 % when the amplitude was 6.55 μm and 1.31 μm, respectively. The fracture mode evolved from ductility dimple fracture to a mixed-mode of cleavage pattern and brittle fracture. The metallographic organization revealed a “defective phase” structure in the α2 phase and B2 matrix. The amounts of defective phases enlarged with amplitude increasing and extended away from the vicinities of the fracture cross-section.