Effect of introducing carbon fiber into AgCuTi filler on interfacial microstructure and mechanical property of C/C-TC4 brazed joints

Highlights: • The intermetallic compounds formed on carbon fiber were characterized in detail. • The formation of brazing interface was systematically discussed. • The effects of carbon fiber content on the microstructure evolution and mechanical property of the joints were investigated. • The strengthening mechanism of carbon fiber during the brazing process was illustrated. -- Abstract: In this work, carbon fiber was introduced into the Ag-26.7Cu-4.5Ti (wt%) filler to optimize brazed joints by participating in brazing reaction process. The interfacial microstructure was analyzed by SEM and TEM, the effects of carbon fiber content on the microstructure and mechanical property of brazed joints were studied, the formation of brazing interface was systematically discussed, and the action mechanism of carbon fiber was illustrated. Experimental results demonstrated that carbon fiber reacted with Ti to generate TiC during the brazing process, and formed a structure of carbon fiber wrapped by TiC and Ti-Cu compounds (TiCu+Ti₃Cu₄). Due to competitive reaction between carbon fiber and Cu to Ti, the formation of bulk Ti₃Cu₄ and TiCu₄ was inhibited, while the formation of Cu-based solid solution was promoted. The microstructure of joints was dispersed as the increase of carbon fiber. The maximum shear strength of 27.8 MPa was achieved when 0.3 wt% carbon fiber was added into AgCuTi filler. The reinforcing effects of carbon fiber were mainly to relieve the residual stress generated by CTE mismatch and reduce the thickness of brittle TiC layer close to C/C composite. However, excessive carbon fiber would deteriorate the joints because of the insufficient reaction between filler and C/C composite.