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 microstructure 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.