Flash sintering phenomena, which occur by applying DC current directly to ceramic powder compacts, can succeed to lower the sintering temperature of several ceramic powders. Spark-plasma-sintering (SPS) is also regarded as one of the external current applied sintering methods under pressure conditions. For the SPS method, since the sintering takes place mainly through deformation processes, especially in the initial and intermediate stages, the understanding of the effect of current on the deformation is important. Conrad and his colleagues examined the effect of electric fields on the tensile properties of 3Y-TZP and confirmed that the fields can lower the tensile flow stresses enough to attain superplasticity. The enhanced deformation was explained by suppressed grain growth due to the electric bias effect. However, since they did not measure real sample temperatures that is necessary for the discussion, the effect of electric field on the high temperature deformation is still unclear. In order to clarify the effect of electric current on high temperature deformation, therefore, the present study was examine the tensile behavior under the several electric field/current conditions using 8mol% Y2O3 stabilized cubic ZrO2 (8Y-CSZ) polycrystals as a reference material.
By applying the electric current higher than a critical value Ec, flash event similar to that of powder sintering occurs even in the bulk 8Y-CSZ. The Ec value is about 100-200 mW/mm3 at around 1000 °C. For lower than Ec, the applied electric current increases sample temperature depending on the applied value, but does not enhance the rate of deformation. For higher than Ec, the electric current enhances the rate of the deformation to about 10 times as compared with that of without current conditions. The enhanced deformation cannot be interpreted only by the increment of sample temperatures and is likely to occur by the flash event. In the presentation, we will discuss the detailed current effect obtained at wide range testing conditions.
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