Study On Preparation And Properties Of Silicon Carbide Based High Performance Ceramics By Foam Billet System

SiC（silicon carbide）ceramics have the characteristics of excellent oxidation resistance,strong high-temperature mechanical properties,excellent corrosion resistance,strong wear resistance and excellent heat conduction.They have attracted extensive attention in the fields of aerospace,machinery manufacturing,petrochemical industry,nuclear energy and electronic technology.Therefore,this experiment takes nano SiC powder and Si powder as the main raw materials based on particle stability The foam mechanism was modified by using cationic surfactant sixteen alkyl three methyl ammonium bromide（CTAB）for hydrophobic modification of SiC powder and pure Si powder.SiC and pure Si foam were prepared by direct foaming method,and SiC and Si₃N₄ foam ceramics were pre fired.On the basis of SiC foam ceramics,SiC high performance ceramics with high density and excellent properties were obtained by hot pressing and sintering SiC foam ceramics with various parameters.In this thesis,the experimental contents are studied as follows:（1）The micromorphology,structure and composition of sintering SiC foam billet at different prefiring temperatures were studied.The results showed that YSi O₂N was generated at the prefiring temperature of 1600℃,and abnormally growing grains on the SiC foam ceramic pore wall were observed by SEM.（2）The phase composition and the morphology of different crystalline nanofibers of sintered pure Si foams under nitriding reaction at different temperatures of 1450℃sintering were studied.The results show that the main forms of Si₃N₄ crystal phase are different when different sintering additives are added.When sintering additive isα-Al₂O₃ andγ-Al₂O₃,Si is mainly needle like after nitridingβ-Si₃N₄ exists in the form of.When the sintering additive is silica sol,Si nitrided mainly presents nano diameter fibrous structureα-Si₃N₄ exists in the form of.（3）Structural morphology,density and mechanical properties of SiC high-performance ceramic materials under different sintering parameters.It was found that when the prefiring temperature is 1450℃,the comprehensive performance of SiC high-performance ceramic material reaches the best,and the bending strength can reach567.22 MPa,and the fracture toughness can reach 5.47 MPa·m^1/2.The SiC high-performance ceramic material prepared at a hot pressure sintering temperature of1900℃has a bending strength of 649.70 MPa.The bending strength of SiC high-performance ceramic material prepared at a thermal pressure sintering pressure of50 MPa pressure reached 601.71 MPa.At the same time,the introduction of Si₃N₄nanowires is obvious,improving the comprehensive mechanical properties of SiC-based high-performance ceramic materials.Under 1450℃prefiring,1800℃30 MPa thermal pressure formula,bending resistance was increased from 567.22 MPa to 664.93 MPa and fracture toughness from 5.47 MPa·m^1/2 to 6.56 MPa·m^1/2.