Atomic force and scanning electron microscopy study of zirconia-coated silicon carbide fibers

The peculiarities of morphology of the initial Hi-Nicalon™ and Tyranno-SA™ fibers and also the zirconia-coated fibers before and after exposition to air at 1000 °C were studied using atomic force (AFM) and scanning electron microscopy (SEM). The quantitative AFM analysis allowed us to evaluate a number of roughness parameters of the initial and coated fibers. After application of coating, the roughness of Tyranno-SA™ fiber was increased approximately by a factor of 2 in comparison with that of the initial fiber for the same scanned squares, whereas the roughness parameters of Hi-Nicalon™ fiber retained its value after application of coating. Moreover, the difference in the roughness parameters for coated Tyranno-SA™ and Hi-Nicalon™ fibers is enhanced after exposition to air at 1000 °C. The grain sizes of coatings are also greatly distinct for both types of the coated and exposed to air fibers. It suggests that the microstructural properties of coatings studied are greatly dependent on the properties of fiber itself. The martensitic relief for the zirconia coating on Tyranno-SA™ fiber was directly observed by AFM.The obtained results on roughness of coated ceramic fibers could be useful for the evaluation and optimization of the mechanical behavior of CMC's, e.g. SiC/ZrO2/SiCf.