Grain boundary phenomena in partially stabilized zirconia polycrystals

The microstructure and chemistry of the grain boundary (GB) migration proce ss was investigated in ZrO2 with the addition of 12 mol.% (17 wt.%) CeO2 an d 1 mol.% (0.8 wt.%) La2O3, as well as in ZrO2 doped with 3 mo1.% (5 wt.%) Y2O3 ceramics by means of the scanning and transmission electron microscopy combined with an energy dispersive X-ray microanalysis. The investigation showed that during annealing at 1775 K, the GB migration is accompanied by the change of the solute content within the zone left behind the boundary. For ZrO2 + CeO2 the zone is Ce and La enriched showing similarity to alloyi ng case of diffusion induced grain boundary migration. The successive backw ard movement of the GB results in the decrease in Ce and La content. In ZrO 2 + Y2O3 after 1 hour annealing, the area swept by the moving boundary is s trongly enriched in yttrium while prolonged annealing (100 hours) results i n the formation of the transition zone with variable yttrium content which resembles so-called precipitate free zone. In some grains the formation of the plate-like structure with approximately the same cerium and yttrium con tents as those in the matrix, was identified as martensitic transition of t he tetragonal phase to monoclinic one.