Vacuum brazing of TZM alloy and graphite with Ti-35Ni alloy: Microstructure, properties, and mechanism

In the present work, a reliable TZM/graphite heterogeneous joint was prepared by vacuum brazing with Ti-35Ni alloy. The influence of brazing temperature on the interfacial microstructure, shear strength, and fracture characteristics of the joints were analyzed. The formation mechanism of the joints was also investigated in detail. TiC layer was formed on graphite during the vacuum brazing process, characterized by SEM and TEM analysis. The interfacial microstructure of the joints brazed at 1200 °C was TZM/Ti(s,s)/TiNi + Ti2Ni/TiC/graphite. The thickness of TiC layer gradually increased with the increase in brazing temperature. In addition, the shear strength of TZM/graphite heterogeneous joints increased first and then decreased, reaching the peak value of 14.5 MPa at 1300 °C. Under optimal vacuum brazing temperature, the fracture path of the joint started in the TiC layer and then extended to the interior of the graphite substrate.