Processing and microstructure of SiC laminar composites

Porous laminar materials and alternate laminates of dense and porous layers in silicon carbide have been elaborated by tape casting and liquid phase sintering (YAG-alumina eutectic) processing. Porosity was introduced by the incorporation of pore forming agents (PFA) (5-50 vol%) in the slurry. Two types of PFA with a narrow size distribution have been used (corn starch and polyamide powders). The effects of size, content, type of PFA on tape casting processing, sintering characteristics, porosity control and microstructure are investigated. For each PFA, the porosity attains a maximum value dependent on the PFA nature (41 vol% with corn starch). Only for starch, the volumetric shrinkage was unaffected by the PFA content up to 45 vol%. Homogeneous distribution of porosity has been obtained for both monolithic and composite laminates. An equiaxed and homogeneous silicon carbide microstructure has been obtained and was unaffected by PFA. Layered structures without defects have been obtained with parallel layers and uniform thickness (dense layer: 70 mum; porous layer: 80 mum). (C) 2001 Published by Elsevier Science Ltd.