The oxidation and scale crystallization kinetics of Hi‐NicalonTM‐S SiC fibers were measured after oxidation in dry air between 700° and 1400°C. Scale thickness, composition, and crystallization were characterized by TEM with EDS, supplemented by SEM and optical microscopy. TEM was used to distinguish oxidation kinetics of amorphous and crystalline scales. Oxidation initially produces an amorphous silica scale that incorporates some carbon. Growth kinetics of the amorphous scale was analyzed using the flat‐plate Deal‐Grove model. The activation energy for parabolic oxidation was 248 kJ/mol. The scales crystallized to tridymite and cristobalite, starting at 1000°C in under 100 h and 1300°C in under 1 h. Crystallization kinetics had activation energy of 514 kJ/mol with a time growth exponent of 1.5. Crystalline silica nucleated at the scale surface, with more rapid growth parallel to the surface. Crystalline scales cracked from thermal residual stress and phase transformations during cool‐down, and during oxidation from tensile hoop growth stress. High growth shear stress was inferred to cause intense dislocation plasticity near the crystalline SiO2–SiC interphase. Crystalline scales were thinner than amorphous scales, except where growth cracks allowed much more rapid oxidation.

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The linear and parabolic oxidation rate constants and activation energies for SiC fibers available in the literature are reviewed for the first time. Oxidation experiments are also conducted with Hi-Nicalon SiC fibers over 700-1 300 C in dry O 2 with thermogravimetric analysis. Linear oxidation kinetics are observed from 700 to 800 C and parabolic kinetics are observed from 900 to 1 300 C. The linear and parabolic oxidation rate constant activation energies are determined to be 83 and 108 kJ mol À1 , respectively. These kinetic results are compared with the literature values. Differences in oxidation behavior are assessed as a function of fiber composition.

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