Preparation And Mechanical Properties Of Silicon Carbide Nanoparticles Toughened Silicon Carbide Ceramics

SiC ceramic materials have many advantages such as low density,high strength,high hardness,high temperature resistance,and fast heat conduction,and have very broad application prospects in aerospace and other fields.However,the shortcomings of SiC ceramic materials such as low fracture toughness and difficulty in densification at atmospheric pressure greatly limit its large-scale production and application in practice.Compared with other toughening methods,the particle toughening preparation process with low cost is simpler and more suitable for large-scale industrial production.In this paper,SiC nanoparticles are introduced into the SiC ceramic matrix to improve the compactness and fracture toughness of atmospheric pressure sintered SiC ceramics,and the mechanism of action of SiC nanoparticles is discussed.Firstly,with SiC submicron powder as the raw material and SiC nanoparticles as the toughening phase,and SiC ceramics with different addition amounts of SiC nanoparticles were prepared by the atmospheric pressure solid-phase sintering method.The compactness and performance of SiC ceramics with different nano-particle additions were discussed.When the addition of SiC nano-particles is 5 wt%,the prepared SiC ceramics had the best performance,with a bulk density of 3.166g/cm³,bending strength of 520 MPa,the Vickers hardness of 22.13 GPa,the fracture toughness of 4.07 MPa·m^1/2,the compressive strength of 3473 MPa and the average linear expansion coefficient within 30℃～1000℃of 4.614×10^-6 K^-1.Secondly,the microstructure of granulated powder,ceramic green body and pre-sintered body in the preparation process of SiC ceramics with different additions of SiC nanoparticles was discussed.The fracture surface of SiC ceramic materials and the crack propagation form when fracture occurred were analyzed.We analyze the enhancement mechanism of SiC nanoparticles from these.Through filling the gaps between some sub-micron particles,speeding up the mass transfer in the sintering process,promoting gas discharge,reducing defects such as pores and promoting densification,a small amount of SiC nanoparticles can improve the bending strength,Vickers hardness,hardness,compressive strength,thermal conductivity and reduce the thermal expansion coefficient of the material.During the sintering process,the SiC nano-particles undergo a phase transformation,which plays a role in phase transformation and toughening.The nano-particles strengthen the grain boundary and cause the ceramic to undergo transcrystalline fracture as well.There is also crack deflection during the fracture process,which increases the crack expanding energy.Thereby the fracture toughness of SiC ceramics is improveng.However,too many SiC nanoparticles will cause the agglomeration of the nanoparticles,which is not conducive to the densification of the ceramics,resulting in the degradation of the ceramic properties.Finally,the practical significance of SiC ceramic toughened by SiC nanoparticles was evaluated.The prepared SiC dry gas seal ring with the addition of SiC nanoparticles of 5 wt%can stabilize the linear velocity at 200 m/s under high-speed rotation,increasing by 20%compared with the limit linear velocity of conventional SiC dry gas seal ring.It also has excellent corrosion resistance and high temperature oxidation resistance.So the SiC_NP/SiC dry gas sealing rings can meet actual needs.