Mechanical Properties And Thermal Shock Resistance Of Pressless Sintered Sic-Based Ceramic Composites

SiC-Al2O3, SiC-Al2O3-Y2O3, and SiC-n-Al2O3 composite with different contents were pressure less sintered at various sintering temperature in nitrogen atmosphere using Silicon Carbide, Aluminum oxide, Nano-Aluminum oxide and Yttria. The composites were characterized by XRD, SEM and Three-point-bending test, Single-edge-notched-beam method, water quenching were also used to test the thermal shock resistence of the materials. The effects of Al2O3, (Al2O3+Y2O3) and n-Al2O3 comtent on the microstructures and properties were investigated.The results show that, for the SiC-Al2O3 composite formed by isostatic cool pressing and sintered at 2100℃for 1h, the relative density of the material show a upward trend as the addition of Al2O3 increase at first, and then turn down as the addition of Al2O3 increase further. The relative density of the composite attain its maximum value, 99.6%, when the content of Al2O3 were 20vol.%. The Young's modulus show a similar trend as the relative density, and also atten its maximum value 423.7GPa, when the content of Al2O3 were 20vol.%. And the flexural strength of the composite get higher as the content of Al2O3 increase. The coefficient of thermal expansion increases as the content of Al2O3 increase, and range from 7.0～7.8×10-6K-1(200～1200℃). The thermal shock resistance of the composite achieve its best performance when the content of Al2O3 is 20%.Compared with the material without Y2O3, the material with addition of Y2O3 get a considerable improvement both in relative density and mechanical properties. And, the relative density show a upward trend as the content of (Al2O3+Y2O3) increase. The YAP phase, a kind of eutectic phase, were formed in the system, the eutectic phase were liquid at the sintering temperature, and prompt the sintering and densification. The mechanical properties of the composite show a upward trend as the content of (Al2O3+Y2O3) increases at first, and then do down. All the mechanical performances of the composite attain its highest value when the content of (Al2O3+Y2O3) were 20vol.%. And the thermal shock resistance of the composite goes upward as the (Al2O3+Y2O3) content go upward.The biscuit of SiC-n-Al2O3 composite were sintered at 2000℃, and high- density composite were prepared. The relative density of the composite attain its highest value, 98.3%, when the content of n-Al₂O₃ were 20vol.%. The flexural strength of the composite go upward as the content of n-Al₂O₃ increases. The Young's modulus and Vickers-hardness both attain their maximum value when the content of n-Al₂O₃ were 20vol.%. But the fracture toughness of the composite attain its highest value when the content of n-Al₂O₃ were 10vol.%. Then as the content of n-Al₂O₃ increases, the fracture toughness goes upward. The coefficient of thermal expansion increases as the content of Al₂O₃ increase, and range from 4.58～5.33×10-6K-1(200～1200℃). The thermal shock resistances achieve its highest value when the content of n-Al₂O₃ is 20vol.%. The addition of n-Al₂O₃ could remarkably improve the microstructure and mechanical performances of the composite, compared with the composite prepared with normal Al₂O₃.