Raman study of yttria-stabilized zirconia interfacial coatings on Nicalon™ fiber

The undoped, 3Y- and 9Y-stabilized ZrO2 interfacial coatings on SiC-based fiber type Nicalon™ were fabricated by sol–gel approach and studied using Raman spectroscopy. Raman spectroscopy proved to be a very successful method for revealing beyond question the monoclinic, tetragonal and cubic modification in the as-prepared and exposed to air ZrO2-coated Nicalon™ fibers. The quantitative phase analysis in the tetragonal or tetragonal/monoclinic two-phase interfacial zirconia coatings was done using an accurate calibration curve directly determined from the Raman spectra of standard mixtures with known monoclinic and tetragonal phase ratios. It was found that the undoped ZrO2 coating on Nicalon™ fiber was composed of monoclinic together with tetragonal modification in approximately equal fractions whereas after exposition to air the t → m phase transformation occurred in full extent. The 3YSZ coating also underwent the t → m transformation, with the extent of this transformation being different for various areas of the same filament and for various filaments.A monitoring of the t → m phase transformation within ZrO2 coating on Nicalon™ fiber using micro-Raman spectroscopy makes it possible quantitatively to evaluate an ability of ZrO2 as oxidation resistance and readily deformable weak interfacial coating for CMC's.