Reaction–formation mechanisms and microstructure evolution of biomorphic SiC

Biomorphic SiC is fabricated by liquid Si infiltration of a carbon preform obtained from pyrolized wood that can be selected for tailored properties. The microstructure and reaction kinetics of biomorphic SiC have been investigated by means of TEM, SEM, EBSD, and partial infiltration experiments. The microstructure of the material consists of SiC and Si and a small fraction of unreacted C. The SiC follows a bimodal size distribution of grains in the micrometer and the nanometer range with no preferential orientation. The infiltration-reaction constant has been determined as 18 9 10-3 s-1. These observations suggest that the main mechanism for SiC formation is solution–precipitation in the first stage of growth. If the pores in the wood are small enough they can be choked by SiC grains that act as a diffusion barrier between Si and C. If that is the case, Si will diffuse through SiC forming SiC grains in the nanometer range.