Flash Sintering Of Ultra-high Purity Alumina Ceramic

Flash sintering,as a new densification technology,has the advantages of low sintering temperature and short sintering time,and has been widely attracted by domestic and foreign researchers.In this paper,the ultra-high pure alumina ceramic materials were prepared by this new technique,and the flash sintering behavior of ultra-high pure alumina ceramics was investigated.The effects of current density,electric field intensity and holding time on microstructure,hardness and fracture toughness of flash sintered ultra-high pure alumina ceramics were studied.The main research contents and results are as follows.（1）The flash sintering behavior of ultra-high pure alumina ceramics was analyzed.In the furnace temperature of 1300℃,the flash event for the ultra-high pure alumina ceramics did not occur at the electric field intensities of 1000～4000 V/cm.When the electric field intensity was increased to 5000 V/cm,after incubation time of1 min,the flash sintering in the ultra-high pure alumina ceramics occurred.Kept an electric field intensity at 5000 V/cm,the influence of furnace temperature on the incubation time of ultra-high pure alumina ceramics was studied.It is found that the incubation time of the sample at the furnace temperature of 1200℃was approximately 901 s,when the furnace temperature was increased to 1300℃,1400℃,the incubation time decreased to 60 s,1s,respectively.This indicated that the furnace temperature had an important effect on the incubation time for flash sintering in the ultra-high pure alumina green body.The conduction activation energy of the dense ultra-high pure alumina ceramics before and after flash treatment shows no change,indicating its conduction mechanism was not changed.The increase in conductivity of the dense sample after flash treatment was mainly related to the increase of oxygen vacancy concentration under the action of electric field.（2）The effects of current density on microstructure,hardness and fracture toughness of flash sintered ultra-high pure alumina ceramics were investigated.When the current densities increased from 5 m A/mm²to 10 m A/mm²,the density,hardness and fracture toughness of the flash sintered samples increased,and the highest density,hardness and fracture toughness were found to be 97.86%、20.39 GPa、3.7 MPa.m^1/2,respectively.When the current density was further increased to 13 m A/mm²,the density,hardness and fracture toughness of the samples decreased.The SEM results showed that the grain size of the samples increased from 280 nm to 360 nm with current density increasing from 5m A/mm² to 13 m A/mm².（3）The effect of electric field intensity on microstructure,hardness and fracture toughness of flash sintering ultra-high pure alumina ceramics was studied.It was found that when electric field intensity increased from 5000 to 7000 V/cm,the density of the flash samples increased from 91.2%to 96.4%,the hardness increased from 16.87 to18.65 GPa,and the fracture toughness increased from 3.18 to 3.51 MPa.m^1/2.The SEM results show that when the electric field intensity increases from 5000 V/cm to 7 000V/cm,the grain of the flash sintered samples did not grow,which may be related to the shorter flash sintering time.（4）The effect of constant current time on microstructure,hardness and fracture toughness of the flash sintered ultra-high pure alumina ceramics was studied.It was found that the holding time prolong from 1 to 60 s,the density,hardness and fracture toughness of the samples increased,and the highest density,hardness and fracture toughness were found to be 97.86%、20.39 GPa、3.7 MPa.m^1/2,respectively.When the holding time was further increased to 90 s,the density,hardness,and fracture toughness of the flash sintered samples decreased.The SEM results showed that the grain size of the samples increased from 228 nm to 370 nm when the holding time increased from 1 s to 90 s.