Tetragonal reconstruction and monoclinic variants rearrangement during heat treatment in zirconia

An in situ monoclinic variants selection and rearrangement study on Y2O3-ZrO2 coatings was conducted using electron backscattered diffraction. The sequence growth of variants with the correspondence of (100)(m) similar to// (010)(t), [010](m) similar to// [001](t), and [001](m) similar to// [100](t) (CAB-OR2) was found initially and converted to the 90 degrees-rotated sequence growth with (100)(m) similar to// (100)(t), [001](m) similar to// [001](t), and [010](m) similar to// [010](t) (ABC-OR2) after heat treatment. In another coating, most of the variants first exhibited interleaving growth and changed to typically fourfold growth. This in situ evolution of both variants orientation relationship and arrangement revealed the effects of stress and stress relief on the martensitic transformation. Moreover, the variants selection might be diversified during the cyclic transformation, and the classical phenomenological theory could mainly be proved by the transformation triggered by temperature, instead of external stress. Furthermore, the variants orientation relationship was exactly confirmed by the tetragonal grain reconstructions. In particular, the orientation variation of reconstructed tetragonal grains was also found and could mainly be explained by the behavior of stress relief and dynamic recrystallization.