Study on structural evolution of nanostructured 3 mol% yttria stabilized zirconia coatings during low temperature ageing

In the present work, the nanostructured 3 mol% yttria stabilized zirconia coatings were deposited by plasma spraying, and its structural evolution during the low temperature ageing in wet atmosphere was investigated by Raman spectroscopy. The results showed that the nanostructured 3 mol% yttria stabilized zirconia coatings had lower resistance to low temperature ageing, although the nanostructured coatings have a metastable tetragonal-prime (t′) crystal structure. The degradation mechanism was explained in terms of the diffusion of oxygen vacancies and OH− ion and the reactions between OH− and Y′ZrY′Zr ion. The microstructure of as-sprayed coating, especially the microcracks, plays a very important role in the low temperature degradation. It can enhance and accelerate the low temperature degradation. It was also verified by wavelength dispersive spectrometer (WDS) analysis that an yttrium-rich surface was formed due to the reaction between OH− and Y′ZrY′Zr ion, which resulted in the transformation of t′ to monoclinic zirconia phase.