Mechanical and corrosion performance of SiC multilayer containing porous layers

Presently, one of the most interesting approaches to the generation of H2 is based on sulphur-based cycles, that however require structural components able to work in a corrosive environment at high temperature. Silicon carbide (SiC) is one of the most promising materials for this application, and to increase its limited toughness multilayered structures can be envisaged, since crack deviation and delamination increase energy adsorption during fracture. In this work tape casting and pressureless sintering were used to produce SiC samples consisting in alternating dense and porous layers, the porosity being realised by the insertion of pore forming agents during the preparation of the green ceramic. The mechanical properties of these materials were studied both at room temperature and at 1550 °C. The effect of corrosion at 850 °C by a mixture of H2O, O2 and SO2 was studied by comparing microstructure and mechanical behaviour before and after long-term (1000 h) corrosion treatments. Corrosion resistance was very good, and flexural strength was strongly increased due to a combined effect of crack tip blunting and compressive residual stress formation. Concerning the architecture instead, the insertion of porous layers brings to a reduction of flexural strength, while Young's modulus remains almost constant.