Abstract
Reaction-bonded silicon carbide (Si-SiC) is potentially promising as a ceramic for use in large-scale structural components in very aggressive corrosion environments. Protective silica scale consisting of amorphous and crystalline layers, se-called bilayer scale, formes on Si-SiC in thermal oxide environments. Thermal cycling may induce severe cracking in crystalline but not amorphous layers due to thermal expansion mismatch between the two layers and the Si-SiC substrate. The amorphous layer is desirable as stable protective scale. Si-SiC samples with silica bilayer scale were heat-treated to study scale thermomechanical stability, then analyzed using SEM and EDX. The mechanical properties on scale Young's modulus and hardness, were measured using depth-sensing microindentation technique. The 1300°C heat-treatment up to 50hr did not affect the bilayer silica scale structure, i.e., no transformation occurred between crystalline and amorphous layers. The Young's modulus and hardness of scale increased with heat-treatment. Change is related to impurity content of Al and K in scale, which was decreased by heat treatment and corresponds to the dependence of silica bulk mechanical properties in the chemical composition.
