The Strengthening And Toughening Of Reaction Bonded Boron Carbide Ceramic Composites

The preparation of boron carbide composites with reaction bonding method has a large amount of advantages such as low sintering temperature?short sintering time and near net shape sintering and so on;and these merits attract researchers from various countries to carry on research on boron carbide composites.However,compared with traditional fabrication method HP(hot pressing)and SPS,the major phase in boron carbide composites prepared by this method losts a lot,and there still exists a mass of free silion in the target ceramics whose properties are far lower.Therefore,the application and popularization of the reaction bonded boron carbide ceramics are restricted.For the purpose of lowing the free silicon?reducing the reaction consume of boron carbide and enhancing the mechanical properties,the influence of particle size distribution on density of green body,phase compositions,microstructure,volume density and mechanical properties of RBBC composites was studied.Based on particle size distribution,the gel casting process of high solid loading B4C-water slurry and the microstructure and mechanical properties of gel casting RBBC composites were investigated.The achievement of this paper are of great significant to the application and promotion of low cost RBBC ceramic composites.The main conclusions are as follows:(1)With the increase of large particle boron carbide content,the density of green body increased;the Vickers hardness of the composites improved while the flexure strength fracture toughness and volume density of the composites decreased.The experimential results show that:when the ratio of B4C powders with different particle sizes(45 ?m:20 ?m:10 ?m:3.5 ?m)is 2.9:1.4:4.3:1.4,the RBBC composites show the most outstanding performance where the Vickers hardness,flexure strength,fracture toughness and volume density are 27.9±4.8 GPa,320±27 MPa,3.9±0.16 MPa·m1/2 and 2.51 g/cm3.(2)With 0.15 wt%dosage and pH value of 11?12,B4C-water slurry with solid loading up to 65 vol%can be obtained,while its viscosity is only 1.6 Pa·s.(3)The structure of RBBC composite prepared by gel casting is more uniform than that by dry pressing,while its comprehensive properties are declined to 26.5±4.3 GPa,345±25 MPa,3.8±0.16 MPa·m1/2 and 2.50 g/cm3,respectively.