Joint Microstructure and Performance of Brazing Si 3 N 4 ‐MoSi 2 Composites to Nb with AgCuTi and AgCuTi+MoSi 2p Active Fillers

MoSi 2 particle (MoSi 2p ), the component of Si 3 N 4 ‐MoSi 2 composites, is added into an AgCuTi filler to strengthen the interface bonding without bringing new elements into the Nb/Si 3 N 4 ‐MoSi 2 brazed joint. In this new brazing system, microstructure evolution and strength of Nb/Si 3 N 4 ‐MoSi 2 joints as a function of brazing temperature and holding time, as well as MoSi 2p content, are investigated. With an AgCuTi filler, the reaction of active Ti and Si 3 N 4 ‐MoSi 2 forms a composite layer consisting of Mo 5 Si 3 , TiN, and Ti 5 Si 3 at the interface. The extensive growth of the layer is observed from 1.9 μm at 860 °C to 5.0 μm at 920 °C, and from 1.3 μm for 5 min to 4.6 μm for 20 min as the chemical reactions between Ti and Si 3 N 4 ‐MoSi 2 are more sufficient. Adding 6 wt% MoSi 2p to the filler, the joints exhibit a peak shear strength of 154 MPa, an increase of 20% over that of a commercial AgCuTi filler, with the fracture path changing from the Si 3 N 4 ‐MoSi 2 to the brazing seam. The enhancement of the joint is attributed to the reinforcement of the seam by in situ reaction of the dispersed MoSi 2p with Ti, refining the microstructure and reducing the thickness of the Mo 5 Si 3 +TiN+Ti 5 Si 3 reaction layer.