Formation of β‐SiAION as an Intermediate Oxidation Product of SiC–AIN Ceramics

The oxidation mechanisms in SiC‐AlN solid solutions, exposed at 1370°C for 200 h in air, have been investigated by scanning electron microscopy (SEM), analytical and high‐resolution electron microscopy (HREM), and X‐ray diffraction techniques. Five hot‐pressed compositions, including pure SiC and pure AIN, were examined. Assuming parabolic rate behavior, the values of the parabolic rate constants based on oxide layer thickness increased by over 2 orders of magnitude by increasing AIN contents from 0% to 62%. A continuous amorphous phase containing cristobalite and mullite crystallites was present at the oxide layer in 13% AIN and 27% AIN samples. Two reaction layers were found in the oxidized SiC–62% AIN solid solution. The inner layer consisted of a mixture of β‐SiAION and graphite phases, while the outer layer consisted of mullite as a major phase and cristobalite as a minor phase. The oxidation proceeded in two stages: a partial oxidation of SiC–AIN to β‐SiAION and carbon (graphite), and a final oxidation of β‐SiAION to mullite + SiO 2 .