Yttria‐stabilized (8.6 mol% YO 1.5 ) zirconia thermal barrier coatings evolve at high temperatures from the “non‐transformable,” metastable tetragonal‐prime phase in their as‐deposited condition to a mixture of the tetragonal and cubic phases. The kinetics of the transformation at 1200° and 1425°C are reported based on X‐ray diffraction measurements. Complementary Raman spectroscopy measurements indicate a sharpening of the tetragonal bands at 263 and 465 cm −1 that is attributed to a systematic decrease in disorder of the Y 3+ and oxygen vacancies with annealing. No transformation to the monoclinic form of zirconia is observed immediately after high‐temperature treatment. However, partial transformation to monoclinic occurs after a prolonged time (months) at room temperature in those samples treated at 1425°C, indicating the development of isothermal martensite.
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Lughi et al. (2005) studied this question.