Effect of Yb2O3 on superplastic behavior of laser welded joint of TC4 titanium alloy

The inhomogeneity of joints during superplastic deformation greatly limits the application of laser beam welding/superplastic forming (LBW/SPF). In order to adjust the deformation uniformity of the joint, Yb₂O₃ with different mass fractions was added to the laser welded joint of TC4 titanium alloy, and the effect of Yb₂O₃ on the superplastic deformation behavior of the laser welded joint of TC4 titanium alloy was studied. The results showed that the addition of Yb₂O₃ can effectively refine β grains. At Yb₂O₃ content of 6 wt%, the refinement effect of Yb₂O₃ on the weld grains is the most obvious. At this time, the peak flow stress of the longitudinal weld sample reaches a minimum value of 25.6 MPa, and the superplasticity of the joint is significantly improved. The elongation of the transverse welded sample reached 29% of that of the base metal and the joint deformation uniformity was significantly improved. The prior β grain of weld broke during superplastic deformation, and the acicular martensite structure in the weld was gradually transformed into a lamellar structure. After the addition of Yb₂O₃, the lamellar structure inside the weld becomes short and disordered, which promotes occurrence of superplastic deformation.