In Situ Observation of Deformation Behavior in a Ti600/Ti₂AlNb Electron Beam Welded Joint

A comprehensive study on the deformation and fracture behaviors of the Ti600/Ti₂AlNb welded joint with diverse microstructures was conducted by room temperature tensile test and in situ tensile test, and the influence of microstructural characteristics on the plastic deformation, crack initiation and propagation of the welded interface has been revealed. Room temperature tensile tests reveal that the negligible disparities in microstructural types among samples processed differently lead to similar uniform deformation capabilities, manifested in adjacent elongations of 6 and 7.3%, respectively. The significant contrast in microstructure between two regions of fracture forged isothermally at 1010  and 975 °C results in distinct levels of dislocation slip difficulty and effective slip lengths, subsequently leading to vastly different reduction of area: 23.5 and 4.5%, respectively. In situ tensile tests reveal that samples isothermally forged at 1010 °C and reheated exhibit a higher maximum engineering strain compared to those forged at 975 °C. Post-forging at 975 °C and heat treatment, microcracks tend to initiate at equiaxed α₂ boundaries, swiftly propagating through the acicular phase to adjacent boundaries, particularly in regions with sparse equiaxed particle distribution. Conversely, large amount of α₂ phase distributions promote plastic deformation at crack tips, leading to a tortuous propagation path. At 1010 °C forging and subsequent heat treatment, microcrack initiation coincides with pronounced plastic deformation, with microcracks forming as the soft lamellar phase tears under external force. These cracks propagate along lamellar α/α₂ tips or cut through parallel lamellae and expand forward.