Microstructure and mechanical properties of linear friction welded dissimilar γ-TiAl/TC17 joints

This study systematically investigates the dissimilar welding of intermetallic compound-based TiAl alloy and titanium alloy TC17 using linear friction welding (LFW), focusing on the microstructural characteristics and mechanical properties of the joints. Under optimized welding parameters, high-quality joints were achieved, exhibiting a tensile strength of 358 MPa and a predominant brittle fracture mode localized at the TC17/TiAl interface. Microstructural analysis identifies three distinct regions: the base metal (BM), the thermo-mechanically affected zone (TMAZ), and the weld zone (WZ). The WZ is characterized by fine equiaxed grains formed through dynamic recrystallization, while the TMAZ exhibits elongated, deformed grains. A well-defined diffusion layer (10–20 μm) is observed at the interface, with a microstructural transition sequence of TC17 (basketweave structure) → equiaxed β → α₂ → γ → TiAl (γ + α₂). The central α₂ layer, measuring less than 5 μm, is identified as the critical factor influencing joint mechanical behavior. Hardness profiling reveals a peak hardness exceeding 500 HV at the weld center, primarily attributed to the α₂ layer. Additionally, the edge region of the joint is prone to three types of microscopic defects—parallel cracks, vertical cracks, and interface voids—which can serve as potential fracture initiation sites, compromising joint integrity.