Grain growth in ultrafine-grained Y-TZP ceramics

Grain growth in dense ultrafine-grained (120–600 nm) tetragonal ZrO2-Y2O3 ceramics is studied as a function of temperature. At all temperatures investigated both segregation and phase partitioning occur. It is argued that at temperatures ≤ 1150 °C grain growth is not significantly inhibited by solid solution drag or by phase partitioning. At higher temperatures the grain growth behaviour can be explained by the models of solid solution drag and/or phase partitioning depending on conditions.\u

Production of defect-poor nanostructured ceramics of yttria-zirconia

For the production of nanostructured ceramics of yttria-zirconia four powders differing in agglomerate strength, agglomerate size and crystallite size are compared. An ultra-fine-grained ceramic with a final density of 98% and a grain size of 0.18 μm could be produced from a hydrothermally crystallized ethanol-washed powder. The remaining porosity is caused by some residual defects which are present due to the irregular shape of the agglomerates and which cause improper die filling. A commercially available powder was also investigated. This powder consists of homogeneous porous, spherical, weak agglomerates. The resulting ceramic has a high density (≥ 99%) but cannot be obtained with ultra-fine grain size (minimum grain size is 0.3 μm). The air-crystallized ethanol-washed powder resulted, after sintering, in larger porosities. In this case the powder consists of weak and some strong agglomerates and a few defect clusters are found in the sintered ceramic which limit the maximum attainable density to 92%. The air-crystallized water-washed powder consists of agglomerates which are too strong to be fractured during compaction. The sintered ceramics contain a large amount of porosity (20%) which is attributed to the presence of inter-agglomerate pores.\u