Interface strengthening mechanism of TZM/Q235 joint by ultrasonic-assisted electron beam welding with high entropy alloy interlayer

The high-strength joints of TZM/CoCrFeNiMo_0.2/Q235 were realized by ultrasonic-assisted electron beam welding. The effects of ultrasonic vibration on the microstructure evolution and mechanical properties of the reaction layers were analyzed. A reaction layer with a thickness of >10 μm was observed at the TZM side region. The reaction layer was characterized by columnar Fe₂Mo phases growing perpendicular to the fusion line and FCC solid solutions with different grain orientations. Under the action of ultrasonic vibration, the eutectic structure of Fe₂Mo phases and FCC solid solutions was evenly distributed in the reaction layer, and the grain orientation of the FCC solid solutions in the reaction layer changed to be the same as that in the fusion zone. Compared with the joint without ultrasonic vibration, the difference of nanoindentation hardness between the Fe₂Mo phases and FCC solid solutions and the residual stress inside the reaction layer of the welding joint with an ultrasonic power of 80 W were significantly reduced. The maximum tensile strength of the joints was 318.4 ± 26 MPa, which was 18.9% higher than that of the joint without ultrasonic vibration.