Preparation And Mechanical Properties Of Alumina Ceramic Composites Reinforced By Carbon Coated Silicon Carbide Nanowires

Alumina ceramics is a kind of engineering ceramics composed of ionic bond and covalent bond which has great application value.Because of its advantages of corrosion resistance,high temperature resistance,and high mechanical strength,which can be applied in the fields of aviation,aerospace and nuclear energy in harsh service environment.However,Al₂O₃ ceramics have intrinsic defects of low toughness,which seriously limit their wide application as engineering ceramics.Improving the fracture toughness of Al₂O₃ ceramics by introducing reinforcing phase has always been a research focus in this field.Silicon carbide nanowires（SiCNWs）are an important reinforcement with high strength,high modulus,high temperature resistance and corrosion resistance.However,SiCNWs have some problems such as easy agglomeration and poor dispersion,which seriously weaken their strengthening and toughening effect.Therefore,this paper proposes to solve the problem of poor dispersion of SiCNWs in Al₂O₃ by coating the surface of SiCNWs with carbon coating and combining with heterogeneous deposition.This paper focuses on the influence of acidizing time on the thickness of carbon layer on SiCNWs surface.The influence of sintering temperature and SiCNWs content on microstructure and mechanical properties of SiCNWs reinforced Al₂O₃ composites was analyzed.The main research contents are as follows:（1）Uniform dispersion and composite of SiCNWs and Al₂O₃ are realized by coating carbon coating and combining with heterogeneous deposition method.The surface modification of sic nanowire was carried out.Firstly,hydrophilic groups were bonded on the surface of SiCNWs by silane coupling agent,and then a smooth layer of phenolic resin was formed on the surface of sic nanowire by in situ polymerization.The sic nanowire coated with carbon layer was obtained by carbonizing the sic nanowire coated with carbon layer.Finally,SiCNWs@C was acidized and modified,and uniform composite alumina and silicon carbide nanowires were obtained by heterogeneous deposition.The carbon content of SiCNWs@C after acidification can be determined by transmission electron microscopy and thermogravimetric analysis.（2）The mechanical properties of sic nanowire reinforced alumina ceramic（SiCNWs@C/Al₂O₃）composite were optimized by adjusting the process conditions.Control variables,first fix the content of sic nanowires in the composite ceramic powder（2 wt.%）,and then change different sintering temperatures to explore the best sintering temperature of ceramic powder.After mechanical test and comparison,it is found that SiCNWs@C/Al₂O₃ composite ceramics sintered at 80 MPa and 1300℃have the best improvement effect on the comprehensive mechanical properties of alumina ceramic matrix,and the bending strength is 5%higher than that of pure alumina ceramics without reinforcing phase.The fracture toughness is increased by 15.4%,reaching 5.77 MPa·m^1/2.（3）After determining the optimum sintering temperature,the optimum doping content of SiCNWs in alumina ceramic powder was explored,the ceramic block was polished,and the mechanical properties were tested.It was found that when 3 wt.%sic nanowires were added to alumina composite,the bending strength and fracture toughness of ceramic materials were increased by 16.4%and 21.0%respectively.