Dispersing,Ultrahigh Pressure Compaction And Pressureless Sintering Of Nano-Silicon Carbide Based Ceramics Composite Powders

Silicon carbide is widely used in industry and chemical and aeronautic industry as a promising room and high temperature structural ceramic,due to its excellent properties such as low density,high hardness,high strength and corrosion resistance.Microstructure,homogeneity,and pore size distribution of green body play an important role in the final properties of sintered body,green body with high relative density and homogeneous microstructure is favorable for sintering nano-phase ceramics.Powder mixture was obtained at by milling highly stable dispersed powders,and silicon carbide green body with homogeneous microstructure and high relative density(>60%)is obtained by ultrahigh pressure compaction by a belt type apparatus and cold isostatic pressing,which was then pressureless sintered to high density,fine grain silicon carbide ceramic.Effect of HF washing and ultrasonication time on particle size and Zeta potential of nano-Si C were analyzed by laser granularity analyzer,Zeta potential analyzer and SEM.Dispersing of Si C and Si3N4 nano particles in mixture of ethanol and ethanediol at different p H.The proportion of ethanol and ethanediol is 100:0,75:25,50:50,25:75,and 0:100 by volume respectively.Laser granularity analyzer was utilized to analyze the relation between sedimentation height and particle size distribution.Conditions for stablely dispersing Si C and Si3N4 simultaneously were obtained.It was found that particle size of nano particles decreased after long time soaking.Processing route for green body of nano silicon carbide based ceramic was investigated.Si C green body with high density(>60%)and homogeneous microstructure was fabricated through dry pressing,cold isostatic pressing and ultrahigh pressure compaction.Microstructure and elements distribut ion of green body was analyzed by SEM and EDS.Si C green bodies with different content of Al2O3 and Y2O3 as sintering additives were sintered in flowing N2 atmosphere by pressureless sintering.Relative density and Rockwell hardness of sintered body were measured,composition,microstructure and morphology of fracture surface were analyzed by XRD and SEM.Effect of sintering temperature,content of sintering additives and ultrahigh pressure compaction on properties of Si C ceramic were discussed.Ultrahigh pressure compaction was found to be effective to increase the relative density of green body to a great extent,which resulted in a high density of sintered body.The residual stress formed in the green body by ultrahigh pressure compaction assisted to confine the grain growth of Si C.Fine grained Si C with relative density over 98% and grain size of ~200nm was obtained by pressurelss sintering ultrahigh pressure compacted green body at 1900℃ for 0.5h.