The Produced Process And The High-temperature Mechanical Properties Of SiC Matrix Composite

SiC has high thermal conductivity,chemical inertia and good mechanical properties at room temperature and high temperature.However,due to its inherent brittleness,SiC ceramics have low fracture toughness and impact resistance,which limits its application in many fields.In this paper,the second phase was introduced into SiC matrix to improve the strength of the material,nano-particle toughened SiC ceramic and carbon fiber?C_f?reinforced silicon carbide composites were prepared,and the microstructure and mechanical properties of the materials were studied.Firstly,nano-particle reinforced SiC ceramic materials were prepared.Taking?-SiC as raw material and nanometer?-SiC as reinforcing phase,the nano-particle reinforced SiC ceramic materials were prepared by pressing-free solid-phase sintering and pressure-free liquid-phase sintering processes respectively,using the transformation of?-?crystal at high temperature.Among them,SiC ceramic materials prepared with phenolic resin and B₄C as sintering assistant have a density of 3.058 g/cm³ and a bending strength of 338 MPa when the content of?-SiC is 10mass%.The fracture mode of the material is a mixed fracture mode of transgranular fracture and intergranular fracture,which will produce resistance to crack propagation along grain boundary,and thus improve the strength of the material.Secondly,C_f/SiC composite material was prepared by chemical vapor phase osmosis method,which has a density of 2.178 g/cm³ and a bending strength of 480 MPa at room temperature.Compared with nano-particle reinforced SiC ceramics,its performance is better,and it is further studied.The failure behaviors of C_f/SiC composites in different atmospheres at high temperature were studied.The results showed that the high temperature oxidation damage of C_f/SiC composites mainly included the oxidation damage of carbon fiber and SiC matrix.Carbon fiber and matrix will be damaged in high temperature argon gas,and the strength of the material will be reduced.With the increase of oxidation temperature,the compression strength of the material decreases.When the temperature is 800?,the compression strength shows a minimum value,which decreases from 246.7 MPa at room temperature to 53 MPa.Finally,the mechanical properties of C_f/SiC composites in high temperature were tested,the coupling analysis of force-hot-oxygen environment the change of material strength,and by observing the microstructure analysis material toughening mechanism,the results show that the material mechanical properties with the increase of temperature of varying degrees of decline,but at 500?,the tensile strength of 253 MPa is higher than at room temperature strength,mainly through crack deflection,fiber pull out the phenomenon such as to improve the strength of the material.And based on the above results,under the same experimental conditions,the first 50 times pre fatigue experiments of the composites,half of the maximum load for the highest strength,then test the temperature of material mechanical properties,the results showed that:after 50times pre fatigue,improves the compression strength,bending strength and the tensile strength declined,which at 1000?,testing the tensile strength,after 41 cyclic load,the material failured.