Green State Joining of SiC without Applied Pressure

Abstract

External pressure (uniaxial or isostatic) is usually necessary to form a thin and defect‐free joint in green state joining of SiC ceramics. A successful method of joining SiC in the green state using a liquid polymer precursor, allylhydridopolycarbosilane (AHPCS), without applied pressure, is described. The thermal decomposition behavior of the polymer was examined, and defect formation during joint evolution was investigated by interrupting the heat treatment at various stages. Cracks and pores were observed in the joints formed by pure AHPCS during the pyrolysis of the polymer precursor. Adding SiC powder to the joining paste eliminated defect formation. Optimum SiC loading in the paste was determined to be in the range of 25–35 vol%. Joints formed by AHPCS + (SiC + 5 wt% B) paste were essentially indistinguishable from the matrix and had an average strength of 323 MPa, comparable to that of the control sample.