Microstructure and properties of different carbon fiber reinforced ceramic composites brazed joint by Si-Ti alloy filler

The brazing of C/C and Cf/SiC composites was achieved using Si-14Ti eutectic filler. The wetting behavior of the Si-Ti filler on the composites, as well as the microstructure and performance of the joints at different brazing temperatures, were characterized. The results showed that the contact angle of Si-Ti eutectic filler on precursor infiltration and pyrolysis (PIP)-Cf/SiC composite surface is only 60 degrees, while it exhibits good spreading effect on liquid silicon infiltration (LSI)-Cf/SiC and C/C composite surfaces. Although Si-Ti filler and carbon fiber reinforced composites (C/C, PIP-Cf/SiC and LSI-Cf/SiC) react to form SiC, the joint shows different mechanical performance. The liquid filler infiltrates into the gaps between fiber bundles and reacts with C/C to form a SiC reaction layer at the interface. However, the presence of numerous defects at the brazed joint between Si-Ti filler and PIP-Cf/SiC results in the shear strength of only 28 MPa for the C/C-PIP-Cf/SiC joint. While for the C/C-LSI-Cf/ SiC joint, due to the residual Si in the LSI-Cf/SiC composites, the liquid filler infiltrates intensely into LSI-Cf/SiC to form a unique Cf/SiC-Si-TiSi2 compound infiltration layer. The shear strength of C/C-LSI-Cf/SiC joints reaches 47 MPa, with fracture occurring in both substrates and brazed seam. The present study offers theoretical support for the investigation of Si-based fillers in brazing carbon fiber reinforced ceramic matrix composites.