During the friction welding process of TiAl turbine and shaft used in engines, brittle intermediate phases will be generated in the welding zone, which affects the joint performance. To reveal the formation rules of the intermediate phases in the friction-diffusion double welding zone between TiAl-based alloy and GH3039 alloy, and investigate the crystal structure and fracture properties of the intermediate phases, the joints at different stages of the double welding were obtained by interrupting welding during the welding process, respectively. The morphology and evolution law of the intermediate phases of these joints in the welding zones were analyzed using SEM; the crystal structures of the intermediate phases and the crack growth behaviors of Al-Ni-Ti ternary intermetallic compound phases were analyzed using TEM and an in situ nanomechanical testing system.Results showed that during friction welding and heat treatment, phase transformation and nucleation occurred on the welding interface and preliminarily grew up to form the following new intermediate phases: Ni₃(Al, Ti), (Ni, Cr)_SS, Al₃NiTi₂, AlNi₂Ti, and Ti₃Al. In the subsequent diffusion welding process, the pressure and high temperature promoted the formation of a stable two-phase zone between Ti₃Al and Al₃NiTi₂. The amplitude-modulated decomposition in the (Ni, Cr)_SS zone formed fcc (Ni)_SS and bcc (Cr)_SS that are staggered and distributed in a column. Dispersions of pure Ti with the α phase could hardly be found in the Al₃NiTi₂ and AlNi₂Ti phases, and the phase boundary between α-Ti and Al₃NiTi₂ was in an incoherent state. Furthermore, Al₃NiTi₂ and AlNi₂Ti exhibited hexagonal and bcc structures, respectively. During the in situ compression process, neither obvious plastic deformation nor dislocation movement was observed in the nucleation and propagation of cracks in the Al₃NiTi₂ phase. However, the lattice surface near the crack tip underwent microdeformation, and the ordered structure of atomic arrangements became disordered.