Preparation And Mechanical Properties Research Of Low- Dimensional Nanophase Reinforced Silicon Carbide Ceramic Composites

Silicon carbide(SiC)ceramic,an extremely important advanced ceramic,has low density(3.21g/cm~3),high hardness,high strength,especially high temperature strength,high thermal conductivity,low thermal expansion coefficient,chemical inertness,high oxidation resistance and wear resistance.These excellent properties have made it become the most important high-temperature structural ceramic materials currently used in aerospace and other fields.However,like other ceramic materials,the biggest disadvantage of silicon carbide ceramics is their inherent brittleness,which makes it extremely limited in the use of structural components.The introduction of a second phase reinforcing material into a SiC ceramic matrix is a common method for improving its mechanical properties,so selecting a suitable reinforcing phase is the key to improving the mechanical properties of the silicon carbide ceramic.Low-dimensional nanomaterials refer to two-dimensional,one-dimensional and zero-dimensional materials other than three-dimensional materials,such as carbon nanotubes(CNTs),silicon carbide nanowires,graphene nanosheets,etc.These materials have excellent properties such as high strength and high modulus,and are ideal reinforcing phases for improving ceramic brittleness.In this paper,carbon nanotubes,graphene nanosheets and silicon carbide nanowires were selected as reinforcing phases,and added to SiC ceramic matrix to prepare SiC ceramic matrix composites.The preparation process,microstructure and mechanical properties of SiC ceramic matrix composites are mainly studied.The results show that the addition of carbon nanotubes,graphene nanosheets and low-dimensional nano-phases such as silicon carbide nanowires can significantly improve the mechanical properties of SiC ceramics,and explore a feasible way to improve the reliability of SiC ceramics.The main research contents of this paper are as follows:(1)In order to solve the problem of agglomeration of CNTs,improve the dispersion degree in the SiC ceramic matrix and the composite effect of CNTs and SiC,firstly,the CNTs were mixed with acid to obtain uniformly dispersed CNTs,and then the SiC powder was modified by APTES.Then,the CNTs and SiC were composited by heterogeneous deposition method.Finally,the dense CNTs/SiC ceramic composites were prepared by SPS sintering process.It was found that the addition of CNTs significantly improved the mechanical properties of CNTs/SiC composite ceramics.When the content of CNTs was 3wt.%,the MSP intensity is 42%higher than that of SiC matrix.In the composites reinforced with 6wt.%CNTs,the fracture toughness showed 31%increase.(2)Firstly,high-quality graphene nanosheets were prepared by microwave-expanded graphite and combined with ultrasonic mechanical peeling method.Then GNSs/SiC ceramic powders were prepared by wet ball milling.Finally,dense GNSs/SiC ceramics were obtained by SPS sintering.The results show that the ball milling time and GNSs content have an important effect on the properties of composite ceramics.Properly extending the milling time will help the dispersion of GNSs in SiC matrix.The suitable GNSs content can significantly improve the strength of SiC ceramics.Finally,it was determined that when the ball milling time was 12h and the GNSs content was 4wt.%,the MSP strength of the composite ceramics increased the most,which was 15%higher than that of the SiC matrix.(3)Based on the preparation of SiCNWs/SiC composite ceramic powder by wet ball milling,dense SiCNWs/SiC ceramic composites were prepared by SPS sintering process.It has been found that the addition of SiCNWs can significantly increase the mechanical properties(especially strength and hardness)of composite ceramics.When the compounding amount of SiCNWs is 5wt.%,the MSP strength is increased by 77%and the hardness is increased by 41%with Relative to the SiC matrix.