Microstructure and deformation mechanism of dissimilar titanium alloy Ti600/Ti22Al25Nb weld joints strengthened by isothermal forging

With the rapid development of the aerospace and civil fields, there are often different performance requirements for different parts of one component. In this paper, we jointed traditional titanium Ti600 and Ti-based intermetallic compound Ti22Al25Nb by vacuum electron beam welding. To improve the weld properties, isothermal forging was performed to strengthen the weld joints. The microstructure after welding and that after isothermal forging were compared, and the mechanism of microstructure evolution was analyzed. The deformation behaviors of the weld joints after isothermal forging were analyzed by the in situ tensile method, and the fracture characteristics were investigated. The results showed that the fusion zone of Ti600/Ti22Al25Nb vacuum electron beam weld joints was a typical dendrite structure, that postwelding heat treatment cannot refine grains, and that the improvement in mechanical properties was limited. During isothermal forging, dynamic recrystallization of grains occurred, and the second phase α2 in the grains was effectively broken. The plasticity and strength of the samples were significantly improved after isothermal forging.