Preparation And Mechanical Properties Of SiC_w Reinforced SiC Ceramics By Gel Casting Process

At present,SiC ceramics biscuit was mostly fabricated by traditional pressing molding.The cracking and deformation of as-products with mass bulk and complex shapes were often caused by the uneven density of the biscuit.Gel casting process was a new molding process based on traditional injection molding technology and polymer chemistry theory.The reactive sintering process showed many advantages such as low sintering temperature,short sintering time and low production cost.SiC whisker reinforced SiC ceramic matrix composites were prepared by gel casting reactive sintering process.The main research work was as follows:the influence factors of slurry rheology,monomer polymerization and green body drying on the process of gel casting were explored;and the effect of SiC whisker reinforced on mechanical properties of reactive sintered SiC ceramics was analyzed.In this paper,the effects of solid content,silicon carbide grain composition,milling time,dispersant content and organic monomer content on the viscosity of the slurry were systematically studied.When the solid content of the slurry was 56 vol%,it could meet the requirements of gel casting process.The effects of initiator content and ambient temperature on monomer polymerization induction period and curing time were investigated.The results showed that solid content and grain composition were the main factors affecting the properties of sintered body.When the solid content was 56 vol%,the sintering density and bending strength of ceramics reached the highest values of 2.94 g/cm³ and 248 MPa,respectively.When W 10:W 14 was 2:1,the viscosity of ceramic slurry was the lowest,and the sintering density and bending strength of ceramics reached the highest values of 2.82 g/cm³ and 223 MPa,respectively.It can be seen from the microstructure that the void fraction and residual silicon phase in the sintered body decreased significantly with the increase of solid phase content,so the sintering density and bending strength were improved.Ceramic biscuit was prepared by gel casting process.SiC whisker were used as reinforcement,and SiC ceramic matrix composites were prepared by reaction sintering siliconized process.The effects of SiC whisker on mechanical properties and microstructure of composite ceramics were discussed.The results revealed that the bending strength and fracture toughness of the sintered samples increased first and then decreased with the increase of SiC whisker content.When SiC whisker content was 12%,the bending strength of the sintered samples reached to maximum of 307 MPa,23%higher than that of matrix samples.When the additive amount of SiC whisker was 9%,the fracture toughness of composite ceramics reached to the maximum value of 3.81 MPa·m^1/2,15%higher than that of matrix samples.The reinforcing mechanism of reactive sintered silicon carbide composite ceramics was whisker pulling and whisker bridging.Whisker pulling and whisker bridge would consume a large amount of fracture energy,at the same time,stress relaxation at the crack tip would slow down the propagation of the crack,which played the role in crack deflection.The addition of SiC whisker enriched the crack growth mechanism during the fracture of reaction sintering silicon carbide composite ceramics and improved the mechanical properties of the composite ceramics effectively.