Properties of Yttria-Tetragonal Zirconia Polycrystal (Y-TZP) Materials after Long-Term Exposure to Elevated Temperatures

Due to an unusual combination of high strength and toughness, tetragonal zirconia polycrystal TZP materials are candidates for use in advanced heat engines. The properties of these materials stem from the stress- assisted transformation of metastable tetragonal zirconia particles. However, after long times at elevated temperatures, this class of materials is susceptible to properties degradation due to the undesirable transformation of tetragonal zirconia to monoclinic zirconia upon cooling. Accordingly, a task was initiated to examine the extent and magnitude of this phenomenons effect on the properties. Seven commercially available yttria-tetragonal polycrystal Y-TZP materials were evaluated. Room temperature properties were measured before and after heat treatments at 1000 C. Microstructure and phase stability were also examined. In all but one case, the Y-TZPs showed very little change in room temperature properties after long times at this temperature. Keywords Ceramic materials, Zirconia, Zirconium compounds, Heat engines, Mechanical properties, High temperature, High strength.