Diffusion bonding of Ti2AlNb alloy using pure Ti foil as an interlayer

In this work, the vacuum diffusion bonding process was employed to robustly join Ti2AlNb alloy using pure Ti foil as an interlayer. The effects of bonding parameters on the interfacial microstructure evolution and mechanical properties of the Ti2AlNb bonded joints at both room temperature and elevated temperatures were investigated in detail. The results showed that the joint consisted mainly of two characteristic zones: diffusion zone I and central zone II, and both these zones were composed of α-Ti and β-Ti phases. The thickness of diffusion zone I as well as the formation of lamellar α and β phases in the central zone II was dependent primarily on the diffusion of the Nb and Al elements from the Ti2AlNb alloy into the Ti interlayer, which was controlled by the modification of bonding parameters. The joint diffusion bonded at 960 °C for 60 min under a pressure of 20 MPa showed a maximum room temperature shear strength of 664 MPa, and its shear strengths at 500 °C, 650 °C, and 800 °C were 442 MPa, 384 MPa, and 305 MPa, respectively. With increases of diffusion bonding temperature and holding time, the shear strength of the Ti2AlNb bonded joints improved owing to the enhanced elemental interdiffusion across the interface. Meanwhile, the fracture path changed from the interface between diffusion zone I and center zone II to center zone II. The fracture morphologies of the joints after the shear tests were characterised mainly by a dimple-like structure, which corresponded to a ductile rupture.