| Because of the low coefficient of thermal expansion, high thermalconductivity, excellent mechanical properties, favorable oxidation resistance andgood corrosion resistance, SiC/Si3N4composites can be used in aerospace, power,petrochemical and many other fields.The SiC/Si3N4composites have been prepared by reactive-hot pressedsintering technique, and the Si3N4, Si and C powder have been used as rawmaterials, MgO and Y2O3have been used as sintering aids. The effects of the Siand C addition and sintering temperature to the composition of phase inSiC/Si3N4composites, microstructure and mechanical properties have beensystematically investigated by X-ray diffraction (XRD), scanning electronmicroscopy (SEM), three-point bending test, single edge notched beam method,etc. The thermal shock resistance of SiC/Si3N4composites have been studied andthe mechanisms for thermal shock resistance of the composites have beendiscussed preliminary.Relative density test results show that with the increaseing of the Si and Caddition, the relative density increase firstly and then decrease. And below thedecomposition temperature of Si3N4, with the sintering temperature increaseing,the relative density of the composites increase gradually.XRD results show that when the sintering temperature is below1800℃,the phase composition of SiC/Si3N4composites are α-Si3N4, β-Si3N4and SiC.And when the sintering temperature is higher than1800℃, the phasecomposition of SiC/Si3N4composites are β-Si3N4and SiC.Mechanical properties tests results show that with the increaseing of the Siand C addition, the fracture strength and fracture toughness increase firstly andthen decrease, but the Vickers hardness shows a steady increasing trend after thefirst change. These properties reaching a maximum value when the Si and C addition is5wt.%. To the composite of which’s Si and C addition is5wt.%, withthe sintering temperature increaseing, the fracture strength and Fracturetoughness increase, but the the Vickers hardness increase firstly then changessteady. These properties reaching a maximum value when the sinteringtemperature is1850℃.SEM analysis shows that the fracture mode of SiC/Si3N4composites isbrittle fracture, and the main fracture mechanisms are intergranular fracture andthe pullout of β-Si3N4. The main toughening mechanisms of the composites arethe dispersion strengthening of SiC particles and the self toughening of β-Si3N4.When the Si and C addition is5wt.%and the sintering temperature is1850℃, the SiC/Si3N4composites have excellent thermal shock resistance. Andthe residual strength in critical thermal shock temperature increased9.6%thanthe single-phase Si3N4ceramic. |
