Hydrothermal corrosion of zirconia-toughened alumina (ZTA) at 200 °C

To investigate the corrosion behaviour of zirconia-toughened alumina (ZTA) under hydrothermal corrosion, a commercial material was compared with materials of similar composition, but fabricated using different processing methods and pure alumina. The specimens were corroded at a temperature of 200 °C in deionised water. Generally, linear corrosion kinetics were found. Pure alumina shows the lowest mass loss and the smallest rate constants. The reduction of the four-point bending strength does not correlate with the mass loss. The main parameter for the degradation is the cubic/tetragonal to monoclinic transformation of zirconia. Investigation of the corrosion of polished surfaces reveals spallation of Al2O3 grains or groups of grains surrounded by zirconia as the main mechanism. A decrease in the size of zirconia grains helps to reduce the strength degradation.