Diffusional cubic-to-tetragonal phase transformation and microstructural evolution in ZrO₂-Y₂O₃ ceramics

The diffusional cubic-to-tetragonal (c-t) phase transformation and microstructural evolution were studied on ZrO₂-Y₂O₃ ceramics with 4 to 6 mol% Y₂O₃ annealed in the two phase (c + t) region for longer periods of time. It was shown that in early stages of annealing a "tweed" structure of t-ZrO₂ was developed. With increasing annealing time this tweed structure becomes coarser and changes into internally twinned "colony" structure. The "colonies" can grow to large sizes but their twin-spacing remains almost constant. The effect of increasing annealing temperature was shown to be more obvious than prolonging annealing time in the transition from tweed to colony structure. The mechanism of the diffusional c-t transformation was discussed.