Research On Oxidation Resistance And Thermal Shock Resistance Of SiC Multiphase Ceramics

In this paper,reaction bond Si₃N₄-SiC and Sialon-SiC are prepared,and their oxidation resistance and thermal shock resistance are systematically investigated by many kinds of test technique and analysis methods such as X-ray diffactometry (XRD),sanning electron miscoscopy (SEM),thermogravimetric analysis (TGA),high temperature MOR-test,stress-strain test and so on.The oxidation kinetics curves have been get from the research of oxidation of Si₃N₄-SiC and Sialon-SiC.And from this research ,we can know that the oxidation processes of Si₃N₄-SiC and Sialon-SiC are controled by the diffusion of O₂,CO and CO₂.From the interpretation of surface topography ,structural constituent and phases etc.,we can get that there are SiO₂, Si2N2O glassy phase and gas cavity on the surface of materials after oxidation,and that the translation of oxygenophilic element from the terior to surface,the existence of impurity and the growth of gas cavity reduce the viscosity of oxidation film which results in acceleration of diffuse speed of O₂,CO and CO₂ and the oxidation speed of specimen.The thermal shock resistance has been deeply studied by the test and measurement of mechanical properties and thermotical properties.The other phase mixed into SiC increases the thoughness of material.The large SiC particles affect crack extension and stress distribution.At high temperature, Si₃N₄ or Sialon phase and free Si become amorphous phase and glass phase which increase elastic deformation ability of material.These above increase the thermal shock resistance.