Microstructure and shear strength of the C/SiC and Q235 brazing joints

C/SiC composites were deposited with Ti coating by magnetron sputtering, and brazed to Q235 with copper interlayer using AgCu₂₈ as filler. The effects of copper interlayer, thickness of Ti coating and brazing temperature on the microstructure and mechanical properties of joints were studied in details. The results show that Cu interlayer can effectively reduce the residual stress of the joint, and obstruct the diffusion of Si element to Q235 during brazing, thus preventing the formation of FeSi_x reaction layer. The thickness of Ti and the brazing temperature both show a peak relationship with the shear strength of the joint. The maximum shear strength achieved 25.5 MPa at 860 ℃ with 3 μm Ti coating. A lager number of C fibers and debonding pits can be observed on the fracture surface at Q235 side. The failure occurs within the C/SiC composite about 300 μm from the interface. The reaction layer at C/SiC interface are mainly composed of Ti₅Si₃ phases containing a small amount of TiC phases. TiCuSi phases are formed in brazing seam.