Development of homogeneous joining techniques for SiC/SiCf composites

The paper reports on the results obtained up to now in the attempt to extend to SiC/SiCf 2-D and 3-D composites the excellent results obtained by joining sintered α-SiC monolithic bodies with pre-ceramic polymer (SR350 silicone resin). The effects on joint performances of parameters such as the heating systems, the pyrolysis temperature, the presence of additives and the inert gas atmosphere were extensively investigated. In order to evaluate the joint quality, shear tests at room temperature were performed on all the joined specimens by means of a modified ASTM D905-89 standard. The best results were obtained by using SR 350 silicone resin with additives. In particular, joints performed by using AI/Si powders showed a maximum value of shear strength of 31.6 Mpa. The adhesive homogeneous bonding technique carried out by a pre-ceramic precursor polymer pyrolyzed at high temperature seems to be very promising for joining SiC/SiCf composites, although the shear strength obtained up to now did not completely satisfy the design requirements. Improvements of the technique are currently under investigation. (authors)