Investigations of the microstructure and mechanical properties of the Nb-Ti/Nb-Ti-Ni brazed joints

The hypereutectic Nb10Ti65Ni25 and eutectic Nb20Ti40Ni40 filler alloys were used to braze Nb-Ti solid solution. It is found that the different filler alloy composition caused different dissolution rates, and consequently formed different interfacial morphology. The Nb10Ti65Ni25 brazed joints showed a relatively flat interface, whereas the Nb20Ti40Ni40 brazed joints displayed an irregular interface due to the isothermal solidification. The micro-structure of the Nb10Ti65Ni25 brazed joints was mainly composed of the Ti2Ni phase and Ti-rich phase. While, the Nb20Ti40Ni40 brazed joints was mainly composed of the eutectic phase, and a small amount of Ti2Ni phase and Ti -rich phase. The room-temperature shear strength of the Nb10Ti65Ni25 and Nb20Ti40Ni20 brazed joints firstly increased with the increase of Ti2Ni phase due to its high shear modulus, however, the precipitation of Ti-rich phase in the brazed joints increased the internal stress, and thus decreased the shear strength. The maximum room-temperature shear strength of the Nb10Ti65Ni25 and Nb20Ti40Ni40 brazed joints were 617.7 MPa and 422.4 MPa, respectively.