In-situ investigation on dislocation slip concentrated fracture mechanism of linear friction welded dissimilar Ti17(α+β)/Ti17(β) titanium alloy joint

In this research, the tensile deformation behavior and fracture mechanism of linear friction welded dissimilar Ti17 (α+β)/Ti17(β) titanium alloy joint were investigated in-depth by in-situ tensile test performed under scanning electron microscopy and further microstructural characterizations using electron backscatter diffraction technique and transmission electron microscopy. The results show that dislocation slip is the dominant deformation behavior of the joint during tensile loading, which occurs in the metastable β matrix and can be impeded by α phase. This effect is concentrating on the Ti17(β) side thermo-mechanically affected zone (TMAZ-(β)), and close to Ti17(β) side heat-affected zone (HAZ-(β)), where a large amount of α is dissolved and transformed into metastable β. The crack initiates from this area owing to microvoids coalescence and propagates along the slip line until fracture. In the other areas of the joint, the relatively high content of α phase, fine grain strengthening caused by dynamic recrystallization, and strain strengthening produced by microstructure deformation, all significantly reduce dislocation slip and hinder crack initiation. Therefore, the fracture mechanism can be attributed to concentration of dislocation slip in TMAZ-(β) close to HAZ-(β), which also results in the tensile strength and elongation of the joint were 1062.1 MPa and 3.5%, respectively, lower than those of the two base metals.