Preparation Of Reaction Bonded Silicon Carbide Ceramics And Reinforcement Of Silicon Carbide Nanowires

The reaction sintering is one of the well-known methods for the preparation of ceramic composite materials because of its low sintering temperature,simple process and low cost.Reaction bonded silicon carbide(RBSC)ceramics are widely used in the areas of safety protection,chemical engineering,aerospace,machinery,metallurgy and electronics because of their excellent properties,such as low density,high temperature resistance,impact resistance and strength.However,the extremely high brittleness of RBSC ceramic material limits its further application.This article focuses on the RBSC ceramic material composition and the addiation of SiC nanowire reinforcement to improve the mechanical properties of silicon carbide(SiC).The results are shown as follows:The microstructure and mechanical properties were improved effectively via using different carbon sources,preparation processes and the adjustment of green body carbon density.With the low density of green body carbon density,the SiC ceramic has high content and large size of the residual Si.It shows the low density and the poor mechanical properties.Continuously increasing the density of green body carbon,the content of Si C increases,the density and mechanical properties of the material reaches to the highest value.With carbon black and phenolic resin used as carbon source,when the density of the carbonaceous material is 0.829g/cm~3,the density of the material is 3.06 g/cm~3,and the Rockwell hardness and flexural strength both reach to the highest values of 90 and 220 MPa,respectively.With the phenolic resin as the carbon source,high performance RBSC ceramic materials is prepared through ultrasonic vibration and mechanical stirring coating by carbon.When the green body carbon density is0.687 g/cm~3,the material density is 2.96 g/cm~3,the Rockwell hardness and flexural strength of the material reach to the highest value of 88 and 250 MPa,respectively.It reveals that controlling the content and size of free Si and Si C particles are effective way to improve the mechanical properties.The mechanical properties of SiC ceramic can be improved significantly with SiC nanowires being the additives as reinforcement.The SiC nanowires can still maintain the original bamboo-like or tower-shaped structure after high temperature reaction,and with the increase of SiC nanowires content,SiC nanowires pullout can be observed in the fracture of the composite ceramics.Compared with the RBSC ceramic without SiC nanowires,the bending strength of the composite ceramic with SiC nanowires are improved significantly.For the composites prepared with carbon black as carbon source,when 12 wt%SiC nanowires are added,the flexural strength of the composites is 300 MPa,increasing by 60%compared with untreated ceramic.For the composites synthesized with phenolic resin as the carbon source,the addition of 10%mass of SiC nanowires leads to the improvement of flexural strength,increasing by 20%and reaching to300 MPa.However,due to the obvious“bridging”phenomenon of excessive nanowires,adding excess nanowires will reduce the density of composite ceramics and limit the further improvement of the composite ceramic mechanical properties.The analysis shows that the mechanical properties improvement of ceramic composite is mainly attributed to the superior mechanical properties of the SiC nanowires and the moderate interfacial strength between the SiC nanowires and SiC ceramic matrix,thus promoting its properties.In a word,optimizing raw materials ratio,adjusting preparation process and adding SiC nanowires as reinforcement are effective way to improve the mechanical properties of RBSC ceramics.The highest bending strength in the experiment is 320 MPa and the highest Rockwell hardness is 90.