The In–situ Mechanical Behavior Of Zirconia Ceramics During Flash Sintering And Its Mechanism Investigation

Flash sintering is a new technology which can realize a rapid densification of ceramics by applying a high electric field.Flash sintering has attracted extensive attention worldwide due to its advantages of low sintering temperature,short sintering time and fast densification speed.Flash sintering is a very complex process with many physical and chemical reactions.Therefore,some unique phenomena and mechanism of flash sintering are still under discovery.In–situ characterization techniques are powerful tools to reveal the scientific essence of flash sintering.In this thesis,an in–situ mechanical characteristic technique was used to realize the relationship between flash sintering and mechanical behavior of ZrO₂ceramics and uncover its possible mechanism.This thesis focused on ZrO₂ceramics（3YSZ polycrystal ceramics and 8YSZ single crystal）.The effect of current density and furnace temperature of flash sintering on the in–situ mechanical behavior was studied.At the same time,two control groups of conventional sintered（no field）3YSZ and single crystal 8YSZ were designed to explore the mechanisms of flash sintering.The phase composition,microstructure were used to reveal the scientific essence of flash sintering induced plastic deformation of ZrO₂ceramics.There are mainly four conclusions of this thesis:（1）When the furnace temperature was 600℃,at low current density（30–50mA/mm²）,3YSZ ceramics exhibit brittle behavior,while at high current density（70–120 mA/mm²）,3YSZ ceramics exhibit plastic deformation.With the increasement of current density（70–120 mA/mm²）,the plastic deformation ability of3YSZ ceramics increases.（2）With the same testing temperature（959–1297℃）,the conventional sintered（no field）samples exhibit brittle behavior.The mechanical behavior of flash sintered samples is significantly different from that of conventional sintered samples,indicating that the flash sintering induced plastic deformation is not only due to Joule heating effect.This comparison also shows the mechanism of flash sintering is not only Joule heating effect.（3）The mechanical behavior and microstructure of 3YSZ ceramics shows that with the increasement of current density（70–120 mA/mm²）or furnace temperature（500–900℃）,the defects,such as dislocations,twins increase.Thus,the elastic modulus,yield strength and hardening index of 3YSZ ceramics decrease due to the synergistic effect of mechanical field,electrical field and thermal field.（4）The higher furnace temperature（≥800℃）,higher current density（≥250mA/mm²）and lower deformation speed（≤0.05 mm/min）are needed to induce plastic deformation of 8YSZ single crystals.Furthermore,a significant amount of dislocations of the 8YSZ single crystal indicate that the plastic deformation of 8YSZ single crystal originates from the movement of dislocations.It also implies that the plastic deformation of 3YSZ polycrystal ceramics is not only due to grain boundary sliding,but also due to the movement of dislocation and/or twins.