Effect of microstructure on the fracture behavior of biomorphous silicon carbide ceramics

Highly porous cellular silicon carbide was prepared from native pine wood tissue by vapor infiltration of Si, SiO, and CH3SiCl3 into the carbonized template. β-SiC at the biocarbon surface finally resulted in a complete conversion of the template into a cellular silicon carbide material. Due to the different reaction mechanisms, different strut microstructures were obtained. The strength of the biomorphous SiC was measured under biaxial tensile loading conditions perpendicular to the cell elongation (in-plane loading). A non-catastrophic stress-strain behavior was observed in the Si and CH3SiCl3 derived materials which showed a high skeleton density of ⩾3 g/cm3. Extendend cell wall fracture (peeling) was observed in the Si derived material where the original intercellular lamella was retained in the ceramic material. FE calculations of the stress distribution in a representative structure model showed significantly lower levels of tensile stress in rectangular pore arrays (early wood tissue) compared to ellipsoidal pores (late wood tissue).