Microstructure and mechanical properties of Ti-48Al-2Cr-2Nb alloy joints produced by transient liquid phase bonding using spark plasma sintering

In the present study, a Ti-48Al-2Cr-2Nb alloy was bonded by transient liquid phase bonding using spark plasma sintering (SPS) process with Ti/Ni/Ti filler metal. It was found that SPS could effectively promote atomic diffusion and hence inhibit the formation of brittle TiNi and TiAlNi intermetallic phases in the joint, resulting in improved joint strength. With increasing the bonding temperature from 1100 °C to 1200 °C, the joint thickness increased from 125 to 206 μm and the microstructure changed from a layered structure into a homogeneous isothermally solidified microstructure. Meanwhile increased amounts of γ lathes and α₂/γ colonies were observed. When the bonding was carried out at 1200 °C, increasing holding time from 5 to 15 min resulted in an increase of epitaxial growth layer thickness from 10 to 25 μm as well as the coarsening of α₂/γ colonies due to solid diffusion. The effects of bonding temperature and holding time on joint strength were studied in relation with the microstructural evolution. The fracture behavior of the joints and the underlying mechanisms were discussed.