TiAl diffusion bonding using Ni/Ti multilayers

Diffusion bonding of TiAl using reactive Ni/Ti multilayers was studied in this investigation. Alternated Ni and Ti layers were sputter deposited onto TiAl base material. These multilayers can be used to improve the diffusion bonding, since they increase the diffusivity at the interface. Bonding experiments were performed at 700 and 800 degrees C under a pressure of 10-50 MPa with a bonding time of 60 min. The interfaces were characterized by high-resolution scanning and transmission electron microscopies. Microstructural characterization reveals that joints can be obtained successfully with Ni/Ti multilayers. The interfaces exhibit slightly different microstructures depending on the bonding temperature and the multilayer bilayer thickness. For all joints, these are mainly composed of equiaxed grains of NiTi and NiTi2. The best mechanical response was achieved for joints processed at 800 degrees C for 60 min under a pressure of 10 MPa using Ni/Ti multilayers with 30 nm bilayer thickness, which exhibit a shear strength of 288 MPa.