Analysis of Microstructure, Fracture Toughness and Crack Propagation Characteristics of Inertial Friction Welding Joint in TC4 Titanium Alloy

The microstructure characteristics in different zones of welding joints at the welding state and post-welding heat treatment state, and the fracture toughness and fatigue crack propagation properties of welding joints were analyzed by XRD, SEM, and EBSD. The results show that the weld zone is mainly composed of recrystallization organization. The equiaxed prior alpha(P) phase is transformed into the rodlike structure in the thermo-mechanically affected zone. The microstructure of the heat affected zone is basically the same as that of the base metal. The acicular martensite alpha' phases with cross angle of approximately 60 degrees are formed within part original beta grains in the thermo-mechanical affected zone and thermal affected zone. After post-weld heat treatment, the residual metastable beta phase decomposes and a large number of discontinuous microstructures are formed between lamellar alpha(S) phases. A large number of parallel or cross distribute flake alpha phases and complex phase interface structure within the alpha grains in weld zone can effectively hinder the crack propagation and change the crack propagation path. Therefore, the fracture toughness and fatigue crack propagation resistance of welding joints are improved.