Joining of C<sub>f</sub>/SiC Ceramic Matrix Composite Using SiC-Si<sub>3</sub>N<sub>4</sub> Preceramic Polymer

Abstract

Carbon fibre reinforced SiC (Cf /SiC) as a promising high temperature structural material possesses broad prospects for aeronautical and astronautical applications. Joining technique is very important from both technical and economical points of view. Joining of Cf/SiC to itself has been realized by reaction joining process using a preceramic polymer, polysilazane, as joining material (welding compound). The weld strength of joints is strongly affected by joining temperature and number of times of reinforcement, which comprises infiltration and pyrolysis of polysilazane. Samples were joined at temperatures ranging from 1100oC -1400oC. The maximum weld strength of joints is obtained at 1250oC. The reinforcement can remarkably increase the weld strength of joints. After three times of reinforcement the shearing strength of joints reaches 27.78MPa. Microstructural study and phase analysis reveal that the joining material has transformed into an amorphous ceramic interlayer composed of Si, C and N at 1100~1250oC, which is uniform and densified. The thickness of the interlayer is 2-3µm. The contact at the interfaces is good without obvious cracks and pores. The amorphous ceramic interlayer transforms into crystal SiC and Si3N4 at 1400oC.