The microstructure and mechanical properties of yttria-stabilized zirconia prepared by arc-melting

The microstructure of ZrO2-Y2O3 alloys prepared by arc-melting was examined mainly by electron microscopy. It was found that the microstructure changed markedly with yttria content between 0 and 8.7 mol%. Pure zirconia was a single monoclinic phase, while ZrO2-8.7 mol% Y2O3 alloy was single cubic phase as expected from ZrO2-Y2O3 phase diagram. Tetragonal phase was found in alloys with 1 to 6 mol% Y2O3 together with monoclinic or cubic phase. The tetragonal phase found in present alloys normally had a lenticular shape with a length 1 to 5 μm and a width 0.1 to 0.3 μm, which is much larger than that formed by annealing. The phase with a herring-bone appearance was found in alloys with Y2O3 between 2 and 3 mol%, which was recognized to be a metastable rhombohedral phase. The structure of the present alloys is likely to be formed by martensitic or bainitic transformation during fairly rapid cooling from the melt temperature. The change in hardness and toughness with yttria content of the alloys is discussed on the basis of microstructural observations. (author)