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 mu m thick diffusion layer formed at the weld interface due to elemental diffusion. The interfacial microstructure was TiAl(gamma)-Ti3Al(alpha(2))-[O+alpha(2)]-Ti2AlNb(O), resulting from diffusion and thermal effects. The highest microhardness was found at the weld interface, where a non-uniform alpha(2) layer of 10 similar to 30 mu m thick was present. This alpha(2) layer is prone to cracking and represents the weak link in the joint.