Effects of air leaks on the phase content, microstructure, and interfacial behavior of CVD zirconia on SiC fiber

A slight increase in the rate of air leaks into the CVD-ZrO₂ process appeared to mitigate the nucleation of tetragonal ZrO₂ phase. Without the nucleation of the tetragonal phase, the ZrO₂ layer was well bonded to the SiC fiber surface and exhibited no delamination at the fiber/coating interface region. This strong bonding at the fiber/coating interface could significantly decrease, depending on the ZrO₂ coating thickness, the tensile failure load of the coated SiC fiber tows. In contrast, ZrO₂ coating specimens, produced at the lower air leak rates, contained the tetragonal ZrO₂ phase. For these specimens, delamination occurred within the ZrO₂ coating, and the coating did not decrease the fiber tow failure load. These results suggest that such a small change in the air leak rate could significantly change the nucleation behavior of ZrO₂ and consequently its interfacial properties as a fiber coating for SiC/SiC composites.