Structure and composition of interlayers in joints between SiC bodies

Joints between SiC bodies (sintered α-SiC and SiC/SiCf composites) which are intended for thermonuclear fusion reactor applications were produced by coating their surfaces with polycarbosilane (PCS) or a silicone resin (GE SR350) alone, or mixed with SiC or Ti powders, followed by heating in an argon flux at temperatures between 900 and 1200°C applying no pressure or a very moderate one (< 0·1 MPa). The joint quality was determined by microstructural and microchemical analyses (TEM, AEM) and by fracture shear tests for comparative evaluations. For SR350, the joining material was a silicon oxycarbide glass, with no oxygen diffusion occurring between this and the SiC joined bodies. The flat interface structure and the lack of any reaction layer suggest that the joining mechanism involves the direct formation of chemical bonds between the SiC bodies and the joining material. Adding SiC or Ti powders does not improve the joining strength. Contrary to silicone resin, polycarbosilane does not serve as an effective joining material, possibly because of its different decomposition behaviour upon pyrolysls. © 1997 Elsevier Science Limited.