Anomalous Temperature Dependence of Cyclic Fatigue‐Crack Growth in a Silicon Carbide Matrix Composite

Fatigue‐crack growth behavior under cyclic tension‐tension loading has been examined in a 30‐vol%‐TiB₂‐reinforced β‐SiC matrix composite, using compact tension specimens tested at temperatures from 750° to 850°C in a furnace air environment. Cyclic fatigue‐crack growth rate was found to depend strongly on testing temperature and was faster at a lower temperature. Such an anomalous dependence of crack growth rate on temperature is shown to result from the reduction in crack growth driving force, ΔK, by the wedging action of the oxide film formed behind the crack tip. Subtraction of the contribution from oxide films leads to a “normal” Arrhenius relation between cyclic crack growth rate and temperature, with the activation energy equal to that for the viscous flow of grain boundary phase.