| SiCf(w)-Cf/SiO2 composites were fabricated by vacuum hot-pressing using carbon fiber, silicon carbide fiber, fused silica powder and silicon carbide whisker as raw materials. The effect of SiCf and SiCw amounts on mechanical, thermal properties and thermal shock resistance of the 10vol%Cf/SiO2 composites is studied by means of XRD, SEM, TEM as well as three point bending and single edge notched beam bending tests.Results show that density and bending strength of composites exhibited a tendency of drop-increase-drop while fracture toughness and work of fracture increased first then drop with the increase of SiCf content. Theα-cristobalite formed as a result of crystallization of fused silica was detected in 5vol%SiCf-Cf/SiO2 composites and its content was up to 42%. The 10vol%SiCf-Cf/SiO2 composites show the best mechanical properties with bending strength, fracture roughness and work of fracture were 97.9MPa, 2.15MPa·m1/2, and 287.2J/m2, respectively.The thermal conductivity increased with an increased addition of SiCf content, and the thermal expansion coefficient increased and then decreased. The composites show good thermal shock resistance, after a thermal shock, underΔT=1100℃, with the minimum residual strength retention of 58.8%.The content of crystallized fused SiO2 was dropped dramatically, and the bending strength, fracture roughness and work of fracture were increase obviously after 5vol%SiCw was added in 5vol%SiCf-Cf/SiO2 and 10vol%SiCw was added in 10vol%SiCf-Cf/SiO2. The elastic modulus of the composites was increased remarkably due to the high modulus of the SiCw..Thermal expansion coefficient of composite was decreased while the thermal conductivity was increased after whisker was added in. And the composites minimum residual strength retention was 56.5% after a thermal shock with△T=1100℃.Investigation on the fractured behaviors of composites, it was found that fracture occurred in the composites was pseudo-plastic fracture, instead of elastic catastrophic fracture. |
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