Mechanical properties and mechanical behaviour of SiC dense-porous laminates

Porous laminar materials and alternate laminates of silicon carbide dense and porous layers have been elaborated by tape casting and liquid phase sintering processing. Porosity was introduced by incorporation of pore forming agents (corn starch or graphite platelets) in the slurry. Homogeneous distributions of porosity have been obtained for both monolithic and composite laminates. The microstructure of the SiC matrix was equiaxed and was not affected by the porosity. The porosity (P) dependence of Young’s modulus (E), modulus of rupture (σR), toughness (K1C) and fracture energy (G1C) was found to be well described on the entire range of porosity by relations of the form X0(1−P)mX proposed by Wagh et al. from a model that takes into account the tortuosity of the porosity. In the case of our materials, mE=2.7, mσR=mK1C=mE+0.5 and mG1C=mE+1. All the ex-corn starch composites behaved in a brittle manner, even those having weak interlayers with a porosity content higher than the critical value of about 0.4 predicted by the model developed by Blanks et al. A non-purely brittle behaviour started to be obtained with ex-graphite laminar composites in which the pores are elongated and oriented parallel to the interfaces.