Joint Microstructure and Performance of Brazing Si₃N₄‐MoSi₂ Composites to Nb with AgCuTi and AgCuTi+MoSi_2p Active Fillers

Abstract

MoSi2 particle (MoSi2p), the component of Si3N4‐MoSi2 composites, is added into an AgCuTi filler to strengthen the interface bonding without bringing new elements into the Nb/Si3N4‐MoSi2 brazed joint. In this new brazing system, microstructure evolution and strength of Nb/Si3N4‐MoSi2 joints as a function of brazing temperature and holding time, as well as MoSi2p content, are investigated. With an AgCuTi filler, the reaction of active Ti and Si3N4‐MoSi2 forms a composite layer consisting of Mo5Si3, TiN, and Ti5Si3 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 Si3N4‐MoSi2 are more sufficient. Adding 6 wt% MoSi2p 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 Si3N4‐MoSi2 to the brazing seam. The enhancement of the joint is attributed to the reinforcement of the seam by in situ reaction of the dispersed MoSi2p with Ti, refining the microstructure and reducing the thickness of the Mo5Si3+TiN+Ti5Si3 reaction layer.