Damage mechanisms of high-temperature titanium alloy laser-welded joints during hot deformation: A multiscale in situ study

Elucidating the damage mechanisms of welded joints during hot deformation holds fundamental significance for the manufacture of high-temperature titanium alloy aviation tailor-welded components. The present study innovatively combines in situ X-ray computed tomography, in situ scanning electron microscopy, and electron backscatter diffraction to systematically investigate the coupled effects of microstructural evolution and welded pores on damage behavior on multiple scales. The presence of welded pores amplifies localized stress concentrations, thereby promoting microcrack nucleation within the cross section. The interaction between initially formed welded pores and surface cracks significantly accelerates fracture propagation. The dynamic globularization of lamellar microstructures reduces localized dislocation density and delays crack initiation. Intergranular crack initiation is mainly related to plastic deformation, which is governed by the synergistic effect of grain boundary orientation and the asynchronous activation of slip systems in adjacent prior β-phase grains. The intergranular cracks tend to nucleate in the direction of maximum shear stress. The differential activation of basal and prismatic slip systems between adjacent grains creates strain incompatibility at soft–hard grain boundaries, ultimately triggering crack nucleation. The present study provides essential guidance for enhancing both formability and service performance in titanium alloy tailor-welded components.