CVI法制备三维碳纤维增韧碳化硅复合材料

THREE DIMENSIONAL CARBON FIBER REINFORCED SILICON CARBIDE COMPOSITES PREPARED BY CHEMICAL VAPOR INFILTRATION

利用三维编织的碳纤维预制体，采用等温ＣＶＩ的方法制备出了碳纤维增韧碳化硅复合材料。对于无碳界面层的复合材料（Ｃ／ＳｉＣ），弯曲强度和断裂韧性随密度的提高而提高，最大值分别为５２０ＭＰａ和１６．５ＭＰａ·ｍ１／２。密度高的复合材料呈明显的脆性断裂，而密度较低的材料在断裂过程中存在纤维束的拔出而表现出韧性断裂行为。密度较高和无碳界面层的复合材料，经１５５０℃高温处理后，弯曲强度明显降低（３５０ＭＰａ），但在断裂过程中由于存在大量的纤维拔出，而表现出韧性断裂行为。存在碳界面层的复合材料（Ｃ／Ｃ／ＳｉＣ）的弯曲强度较低（３００ＭＰａ），在断裂过程中表现出典型的复合材料断裂行为，在断裂过程中既存在纤维束内部的脆性断裂。

Continuous carbon fiber reinforced silicon carbide composites were prepared by chemical vapor infiltration,in which the preforms were fabricated by the three dimensional braid method.The mechanical properties and microstructure were investigated.For the composites without carbon interface layer(C/SiC),flexural strength and fracture toughness are increased with density of the composites.The maximum values are 520 MPa and 16 5 MPa·m 1/2 respectively.The fracture mode is dependent on the interface bonding between fiber/matrix and fiber bundle/bundle.When density of the composites is low,the interface bonding between fiber bundle/bundle is weak which results in bundle pullout during failure of composites.The composites exhibit tough fracture behavior.As the increase of density,the interface bonding between bundle/bundle is also increased.The fracture mode shifts from tough to brittle behavior.After annealed at 1550℃ for 5h in vacuum,the composites with high density and no carbon interface layer also exhibit tough fracture behavior since there exists large amount of fiber pull out.Then the flexural strength is decreased to 350 MPa.The C/PyC/SiC composites with carbon interface layer(C/C/SiC)fail continuously and have a relatively low strength(300MPa).