Preparation And Densification Mechanism Of MgO Doped Al₂O₃ Ceramics By Flash Sintering

Alumina ceramics have been widely used in modern engineering and technology because of their excellent properties such as high hardness,good strength,corrosion resistance,etc.Due to the low self-diffusion coefficient and the difficulty of densification,alumina ceramics usually required long sintering time and high sintering temperature.In order to reduce the sintering time and temperature of alumina ceramics,developing advanced sintering methods is desired.Therefore,in this paper,flash sintering as a new electric field-assisted sintering is used to prepare Mg O-doped Al₂O₃ ceramics,and the main research contents and conclusions are as follows:（1）The effect of current density on the microstructure and mechanical properties of flash sintered Mg O-doped Al₂O₃ ceramics was investigated,and the sintered samples with uniform grain size and high density were obtained at 1300°C with an applied electric field of 2500 V/cm and a holding time of 60 s.As the current density increased from 3m A/mm² to 7 m A/mm²,and the relative density of sintered increased from 96.36%to99.91%.and the grain size varied from 0.65 to 0.76μm;the hardness exhibited a similar variation trend with relative density,while the fracture toughness showed a slight decrease.Among all the flash sintered samples,the highest densities（up to 99.91%）and hardness21.02 GPa)were obtained in the samples flash sintered at a current density of 7 m A/mm².（2）The effect of electric field intensity on the microstructure and mechanical properties of flash sintered Mg O-doped Al₂O₃ ceramics was investigated.The densities increased from 91.92%to 99.36%and then decreased to 94.73%when the applied electric field was increased from 2500 V/cm to 5000 V/cm,and the changes of hardness and fracture toughness also showed the same trend.The highest densities of 99.36%,hardness of 20.89 GPa and fracture toughness of 4.44 MPa·m^1/2 were observed in the flash sintered sample at 4000 V/cm.（3）The effect of holding time on the microstructure of flashed Mg O-doped Al₂O₃was investigated.It was found that with the holding time increased from 0.5 s to 60 s,the densities of the samples increased from 91.92%to 99.91%,the grain size raised from0.23μm to 0.76μm,and the hardness increased from 18.04 GPa to 21.02 GPa.（4）The grain growth and densification behavior of flashed Mg O-doped Al₂O₃ceramics were investigated.It was found that the electric field increased boundary mobility of alumina grain,promoted grain growth.The densification rate of Mg O-doped Al₂O₃ during flash sintering continuously decreased with holding time;the densification rate was large in the flash sintering stage（second stage）,while was small in the stable stage（third stage）.According to the classical densification theory,the densification mechanism in the flash sintering stage should be controlled by the particle rearrangement under the action of electrostatic force,and the densification mechanism in the stable stage should be lattice diffusion.