Diffusion bonding of dissimilar titanium alloys via surface nanocrystallization treatment

A TC17 titanium (Ti) alloy, with and without surface nanocrystallization (SN) treatment was joined to another Ti alloy, TC4, via solid-state diffusion bonding. The interfacial void shrinkage of SN-TC17/TC4 bond was accelerated comparing with that of coarse-grained TC17/TC4 bond. Dynamic recovery and recrystallization were mainly responsible for the fiber texture in β phase and the random orientation in α phase on SN-TC17 side, respectively. The promoted grain growth effect on SN-TC17 side at 1093 K contributed to the disappearance of original bond line (BL). The shear strength of SN-TC17/TC4 bond increased as bonding temperature increased to 1013 K due to the enhanced void shrinkage process, which further increased up to 789 MPa at 1093 K as a result of the disappearance of original BL. Moreover, the shear strength of SN-TC17/TC4 bond at 1093 K was about 60 MPa higher than that of TC17/TC4 bond due to the disappearance of original BL and the Hall–Petch strengthening effect.