Yttria migration in Y-TZP during high-temperature annealing

The microstructural and phase changes occurring during the high temperature (1300 to 1550° CO annealing of Y-TZP were studied using X-ray fluorescence, X-ray diffraction, and TEM. Two processes occurred simultaneously involving the diffusion of yttrium. The Y-TZP partitioned into yttria-rich and yttria-poor phases throughout the material, because the material lies in a two-phase two-phase field of the yttria-zirconia phase diagram. The other process involved the segregation of yttrium to the surface, the extent of which was shown to vary with the state of the surface (ground or polished), annealing temperature, and silica content. Migration of yttrium to the surface caused a significant surface composition change (i.e. from 4.7wt% Y₂O₃ at room temperature to 8.9 wt % Y₂O₃ at 1550°C for 3 h), resulting in a microstructure and phase composition different from the bulk.