High temperature deformation behavior of polycrystalline zirconia under electric current
It has been reported that the application of electric field/current can acceralate high temperature phenomena of ceramic materials. Especially, flash sintering, which occurs by applying DC current directly to ceramic powder compacts, can succeed to reduce the sintering time/temperature of several ceramic powders. Recently, the flash event caused by the electric field/current has been reported to be contributed effectively not only to the sintering phenomena, but also to other high temperature ones. For example, 3Y-TZP is reported to exhibit superplastic flow even at lower temperatures under the flash event condition. However, the effect of electric field/current on the high temperature deformation is still unclear. In order to clarify the field/current effect on the high temperature deformation of ceramics, therefore, the present study was carried out to examine the creep behavior of polycrystalline zirconia ceramics under the several electric field/current conditions.
By applying the electric power higher than a critical value Ec, the flash event similar to that of the powder sintering occurs even in zirconia bulk ceramics. At around 1000 °C, for example, the Ec value is about 100 - 200 mW/mm3, which is slightly larger than those reported in the powder compacts. Under the flash condition, the electric field/current enhances the rate of the deformation to about several times as compared with that of the conventional creep deformation without the field/current conditions. The enhanced deformation cannot be interpreted only by the increment of sample temperatures caused by Joule heating and is likely to be related to the flash event. The field/current effect is related to the microstructure and tends to become more pronounced with fine grained materials. After the deformation under the electric current conditions, the tested sample shows slight gray color even in air, suggesting that the enhanced deformation would be related to oxygen vacancy formation.
Acknowledgments: This work was financially supported by A-STEP program (No: JPMJTS1617) and CREST Program (No: JPMJCR1996), Japan Science and Technology Agency, Japan.