Resistance of InO1.5-stabilized tetragonal zirconia polycrystals to low-temperature degradation

9 mol% InO1.5-stabilized zirconia (ISZ) was synthesized using a coprecipitation method. Sintered samples were hydrothermally degraded for periods of up to 40 h in an autoclave at 134 °C and 2 bar. The tetragonal to monoclinic phase transformation (t-m) was observed by X-ray diffraction (XRD) and atomic force microscopy (AFM). An increase in surface roughness, associated with the martensitic t-m transformation was observed by AFM. According to XRD patterns, 30 vol% of the tetragonal phase initially present in the ISZ sample transformed into the monoclinic phase after the hydrothermal degradation. The impact of the transformation was evaluated in terms of structural integrity. Vickers hardness was not affected, however the flexure strength decreased by about 43% after autoclave treatment for 10 h. A key finding from this study is that, despite a rapid decrease of flexure strength during initial autoclaving step, ISZ presents a lower trend to t-m transformation than the currently used 3 mol% yttria-stabilized zirconia material. The high concentration of oxygen vacancies and low tetragonality of 9 mol% ISZ seem to be responsible for its superior resistance to hydrothermal degradation.