Study On Celcasting Combined With Cold Isostatic Pressing Of Alumina Ceramics

As a kind of wet forming,gelcasting technology combines organic polymer polymerization theory with traditional slip casting,which has great advantages in the field of ceramic parts with complex molding shapes and unlimited sizes.Generally,high density of green body,which means the solids loading of slurry should be as high as possible,is required for high quality ceramic parts.However,the increase of solids loading will inevitably lead to a rapid increase in the viscosity of slurry and deterioration of slurry pouring performance.Then,big pores are easily formed especially in thin-walled large-size or complex-shaped green body,which will eventually deteriorate the performance of ceramic parts.Compared with the high solids loading slurry,the low solids loading slurry is prepared more easily,has lower viscosity and better fluidity,which is beneficial to reduce the possibility of defects forming in green body.For the problem of low density of ceramic green body made from low solids loading slurry,the isostatic pressure of cold isostatic pressing can be used to make up and effectively solve the problem of uneven body.The exploration of molding technology depends on the materials.Al2O3 ceramic material has broad application prospects in engineering fields such as aerospace,wear parts due to its advantages of high mechanical properties,wear resistance,high temperature resistance,chemical corrosion resistance,and low raw material prices.Therefore,this material is selected as the research object for the study of gelcasting combined with cold isostatic pressing.Taking raw materials,green bodies and sintered bodies as the three fulcrums,the gelcasting combined with cold isostatic pressing was systematically studied.Three kinds of domestic Al2O3 powders with different characteristics were introduced.The gelcasting process was used as a molding method to study the influence of raw materials on the properties of slurries and green bodies and then put forward the selective principle or method of Al2O3 raw materials.The effect of cold isostatic pressing parameters on the performance of green bodies and the density of sintered bodies were studied.The density of Al2O3 ceramics formed by this process was compared with it by traditional high solids loading gelcasting process.The results show that:The performance of slurries,green bodies and sintered bodies were highly influenced by the dispersion state of Al2O3 powders.When the powder particle size reaches the nanoscale,it is easy to form agglomerates,which will greatly deteriorate the slurry fluidity,decrease the density and structural uniformity of the green body and sintered body.So powders with small particle size,narrow particle size distribution and good dispersibility are the prerequisites for preparing sintered bodies with high density and uniform structure.With the increase of solids loading,the viscosity of Al2O3 slurry increases.With the increase of dispersant additive amount or the extension of ball milling time,the viscosity of the Al2O3 slurry showed a tendency to decrease first and then increase.There is an optimal dispersant amount and the optimal range of ball milling time make the ceramic slurry's viscosity lowest.The best range of ball milling time is 4?6h in this article.With the extension of pressure retention time,the density of Al2O3 green body increases first and then tends to be gentle.When the pressure retention time is longer than 5min,the relative density of Al2O3 green body will not change.In the range of 0?500 MPa,with the increase of cold isostatic pressure,the relative density of Al2O3 green body increases.At the high pressure of 500 MPa,the green body is still in the second densification stage.With the increase of cold isostatic pressure,the compressive strength of the Al2O3 green body increases first and then basically unchanged.At the pressure of 350MPa,the compressive strength of green body is the biggest.As the post processing,cold isostatic pressing can not only reduce the adverse effects caused by the curing process and improve the macrostructure uniformity of green body significantly,but also can eliminate pore defects by transferring it from the green body inside to surface.With the increase of cold isostatic pressure,the density of Al2O3 ceramics showed a tendency to increase first,then remain unchanged and then decrease.At the pressure of 350MPa,the relative density of Al2O3 ceramics increased to a maximum value.Compared with the high solids loading 53vol%gelcasting process,the density of Al2O3 ceramics is higher by the low solids loading 45vol%gelcasting combined with cold isostatic pressing process.This new forming method can be used to prepare dense Al2O3 ceramic parts.