Interfacial microstructure and bonding strength of diffusion bonded TiAl/Ti/Nb/GH99 alloy joint

Diffusion bonding of TiAl-based alloy to Ni-based alloy using Ti/Nb composite interlayer was carried out. The formation phases and the interfacial microstructure of the joints were investigated by scanning electron microscopy, electron probe X-ray analysis and X-ray diffraction. The bonding strength of the joints was evaluated through shear test. The results show that the typical interfacial microstructure of the joint is GH99/(Ni, Cr) _ss/Ni ₃Nb/Ni ₆Nb ₇/(Ti, Nb) _ss/α-Ti+(Ti, Nb) _ss/Ti ₃Al/TiAl. The maximum shear strength of 273.8 MPa can be achieved under the condition of T=900°C for t=30 min and p=20 MPa. With the joining temperature T increasing, the interfacial microstructure and thickness of reaction layer changes. When the brazing temperature T>900°C, Ni ₆Nb ₇ reaction layer which has bad effect on the bonding strength forms. Based on the experimental results, the formation process of reaction layer was analyzed and interfacial reaction mechanism of the interface of GH99/Nb and Nb/Ti/TiAl was revealed.