Study of microstructure and mechanical properties of Ti₂AlNb/TiAl LFW joint

TiAl and Ti₂AlNb intermetallic alloys are promising alternatives to conventional superalloys due to their high-temperature resistance, which offers potential for energy savings and weight reduction. However, the connection of dissimilar TiAl/Ti₂AlNb is still a challenge. This study investigates the linear friction welding (LFW) of TiAl/Ti₂AlNb alloys under specific parameters: a frequency of 45 Hz, friction pressure of 120 MPa, amplitude of 2 mm, and a welding time of 5 s. The results showed a well-formed joint with a tensile strength of 332 MPa. Microstructural analysis revealed that the joint consists of three distinct zones: the base material (BM), the thermo-mechanically affected zone (TMAZ), and the weld zone (WZ). In the WZ, the grain morphology exhibits an equiaxed crystalline structure, indicating the occurrence of dynamic recrystallization. The zone widths were wider on the Ti₂AlNb side due to differences in thermo-mechanical properties. An 8 μm thick diffusion layer formed at the weld interface due to elemental diffusion. The interfacial microstructure was TiAl(γ)-Ti₃Al(α₂)-[O+α₂]-Ti₂AlNb(O), resulting from diffusion and thermal effects. The highest microhardness was found at the weld interface, where a non-uniform α₂ layer of 10∼30 μm thick was present. This α₂ layer is prone to cracking and represents the weak link in the joint.