Control of the Tetragonal to Monoclinic Phase Transformation of Yttria-doped Tetragonal ZrO2 Polycrystals by Annealing in Water

Abstract

The tetragonal-to-monoclinic phase transformation of yttria-doped tetragonal zirconia polycrystals by annealing in water was investigated at 80–200°C using the sintered bodies of zirconia containing 2, 3 and 4 mol% Y2O3. The tetragonal-to-monoclinic phase transformation accompanied with microcracks and greatly degraded the fracture strength. The fracture strength of the annealed zirconia ceramics depended on the transformation layer thickness. Three approaches, alloying ZrO2(Y2O3) with 0–20 wt% CeO2, dispersing 0–40 wt% Al2O3 into ZrO2(Y2O3) and decreasing the grain size of zirconia were examined to control the tetragonal-to-monoclinic phase transformation. The amount of the monoclinc phase formed decreased with increasing the concentrations of CeO2 alloyed and Al2O3 dispersed, and with decreasing the grain size of zirconia. From the present experimental results, it is expected that the tetragonal-to-monoclinic phase transformation of yttria-doped tetragonal zirconia polycrystals is controlled by the addition of CeO2 and dispersion of Al2O3, and the degradation of the fracture strength by low temperature annealing is completely inhibited.