Fabrication And Properties Of SiC Porous Ceramic Composites By A Novel Approach

Porous silicon carbide ceramics are promising materials, due to their excellent thermal stability, low density. These advantages make porous silicon carbide ceramics having great potential application in various fields, such as thermal insulation, filers, bio-scaffolds and so on. There are many different kinds of fabrication technologies for porous ceramics, but there are many limitations from the high requirements for the raw materials and fabrication facilities by using the conventional fabrication process. And also, the porous ceramics by conventional process generally exhibited poor mechanical properties, which inhibited their futher development and application in some special fields.In the current work, phenolic resin was used as ceramic precursors for the fabrication of SiC porous ceramics. The chopped carbon fibers with different volume fractions were introduced into the matrix to improve the mechanical properties of porous ceramics. Three point bending test and single-edge notched beam were applied to measure the mechanical properties, respectively. The surface morphologies and microstructure and observed by optical microscope and scanning electron microscopy, respectively.The results found that the fabrication approach applied in the present work can successfully prepare the fiber-toughed porous ceramic composites. The fabricated porous ceramics have high porosity, and the porosity is generally increased with the increase of carbon fiber volume fraction. The maximun value of porosity is about 64.54%. The chopped carbon fiber could improve the mechanical properties significantly. The microstructure analysis revealed that the main toughening mechanisms responsible for the high mechanical properties could be attributed to the fiber debonding, fiber bridging and fiber pull out. The bending strength and fracture toughness are increased with the increase of fiber volume fraction. But the high fiber volume fraction will lead to an increase of porosity, which will decrease the mechanical properties of porous ceramics. In the present work, when the fiber volume fraction is 18wt.%, the bending strength and flexural toughness reach the highest value. They are 5.83MPa and 0.35MPa.m1/2, respectively. The chopped fiber reinforced SiC porous ceramics show good toughness, and the maximum value of fracture work is 333J/m2. Furthermore, by increasing Si content, the bonding strength between fiber and matrix could be improved, which leads to an increase of fracture strength. However, the existence of residual Si will decrease the toughness of porous ceramics.