ACOUSTIC-EMISSION STUDY OF PHASE-RELATIONS IN LOW-Y2O3 PORTION OF ZRO2-Y2O3 SYSTEM

The (metastable) tetragonal phase in 3-4 mol % Y2O3-ZrO2 alloys underg oes a transition to the monoclinic form in the 200-300-degrees-C tempe rature range. Microcracking due to the volume change at this transitio n has been detected in these compositions by sharp acoustic emission d uring heating, The phase change was confirmed by X-ray diffraction, di latometry and scanning electron microscopy. The monoclinic half arrow right over half arrow left tetragonal transition in ZrO2-1 mol % Y2O3 alloy at 850-750-degrees-C and the same phase change in 2, 3, 4 and 6 mol % Y2O3 compositions at the eutectoid temperature of about 560-degr ees-C was also clearly signalled by the acoustic emission counts durin g heating and cooling. There was no significant acoustic emission acti vity on heating and cooling the 9 and 12 mol % Y2O3 compositions, whic h are cubic. The acoustic emission data thus confirm the phase relatio ns in the 1-12 mol % Y2O3 region, established by conventional methods such as differential thermal analysis, dilatometry and X-ray diffracti on.