Study On The Preparation Of Alumina Ceramics By Current Ramp Flash Sintering

Flash sintering is a new ceramic sintering technique proposed by Professor R Raj in2010 which is applied electric field at both ends of green sample（high electric field,low current density）.During flash sintering,fast densification of green sample can be realized at a lower furnace temperature.Flash sintering has the advantages of reducing sintering temperature,shortening sintering time and reducing energy consumption.Alumina ceramic is widely used industrial production of high performance ceramics.The sintering of alumina ceramics has the disadvantages of high sintering temperature,long sintering time and abnormal grain growth.For solving the above–mentioned issues,a current ramp flash sintering technique was used which will promote the development of alumina ceramics industry significantly.In this thesis,The main research content is divided into the following three parts:（1）Process parameter optimization:the initial furnace temperature,applied electric field,current density,current ramp and other parameters were studied to optimize the current ramp flash sintering of alumina ceramic and achieve high performance ceramics.（2）Structural characterization and flash sintering mechanism:The density and microstructure of as-obtained alumina ceramics were analysis to reveal processing–structure relationship,such as initial temperature,applied electric field,current density and current ramp.The average grain size,blackbody radiation temperature and sintering force of flash sintered alumina ceramics were analyzed to reveal the flash sintering mechanism.（3）Mechanical properties:The hardness and toughness of the alumina ceramics obtained by flash sintering were tested,and the change trend of the hardness and toughness with current density was analyzed by considering the traditional sintered alumina ceramics as a control group.The main conclusions are shown as follows:（1）The density of alumina ceramics obtained by current ramp flash sintering is higher than that of traditional sintered alumina.Under the traditional flash sintering conditions of 1300°C and 700 V/cm,8 m A·mm^-2,the maximum density of alumina ceramics is96.8%.To the contrary,under the same conditions,the maximum density of the sample obtained by current ramp flash sintering with current ramp of 1 m A·mm^-2·s^-1 and current density of 8 m A·mm^-2 is 98.6%,and the temperature is 300°C lower than that of traditional sintering.（2）The average grain size increases with the increase of current density.In traditional flash sintering,the average grain size is 0.79μm,the average grain size increases sharply when the current density is higher than 8 m A·mm^-2.For the current ramp flash sintering,the average grain size is 0.76μm and no significant grain growth even the current density is higher than 8 m A·mm^-2.（3）The hardness and toughness of alumina ceramics obtained by traditional flash sintering and current ramp flash sintering are obviously higher than that of traditional sintering ones.The hardness of alumina ceramics achieved by traditional flash sintering and current ramp flash sintering are 19.47 GPa and 19.84 GPa,respectively,which are12%and 14%higher than that traditional non–press sintered samples（17.41 GPa）.The corresponding toughness is 4.09 MPa·m^1/2 in traditional flash sintered samples and 4.69MPa·m^1/2 in current ramp flash sintered samples,which is 35%and 55%higher than that of traditional non–press sintered samples(3.02 MPa·m^1/2).（4）The optimized flash sintering process parameters are of applied electric field of700 V/cm,initial furnace temperature of 1300°C,current ramp of 1 m A·mm^-2·s^-1,current density of 8 m A·mm^-2,and the density of as–sintered alumina ceramics is98.6%.