Acoustic emission study of phase relations in low-Y₂O₃ portion of ZrO₂-Y₂O₃ system

Abstract

The (metastable) tetragonal phase in 3-4 mol% Y₂O₃-ZrO₂ alloys undergoes a transition to the monoclinic form in the 200-300 ° C temperature range. Microcracking due to the volume change at this transition has been detected in these compositions by sharp acoustic emission during heating. The phase change was confirmed by X-ray diffraction, dilatometry and scanning electron microscopy. The monoclinic ⇌ tetragonal transition in ZrO₂-1 mol% Y₂O₃ alloy at 850-750° C and the same phase change in 2, 3, 4 and 6 mol% Y₂O₃ compositions at the eutectoid temperature of about 560 ° C was also clearly signalled by the acoustic emission counts during heating and cooling. There was no significant acoustic emission activity on heating and cooling the 9 and 12 mol% Y₂O₃ compositions, which are cubic. The acoustic emission data thus confirm the phase relations in the 1-12 mol% Y₂O₃ region, established by conventional methods such as differential thermal analysis, dilatometry and X-ray diffraction.