两种典型连续SiC纤维的精细微观结构及性能研究

Study on Fine Microstructure and Properties of Two Typical Continuous SiC Fibers

采用SEM、TEM、XRD等表征手段研究了不同温度烧结的两种典型连续SiC纤维高温氧化前后的微观结构和性能.发现高温烧结的F-1纤维结晶度高,从表层至芯部,SiC晶粒尺寸逐步减少;而石墨含量却稍有增多.低温制备的F-2纤维主要为非晶,其中含有大量SiC和石墨纳米晶.F-1纤维存在少量的孔洞,其强度为1.74 GPa,而F-2纤维致密,强度达到2.76 GPa.两种纤维在1000℃空气加热中均发生氧化,且随时间的延长,氧化层增厚,纤维强度降低.虽然高温烧结的F-1纤维含有氧扩散通道晶界,但经10 h氧化后纤维的强度保留率仍能达到55%;低温烧结的F-2纤维抗高温氧化能力差,经10 h氧化后氧化层厚度高达430 nm,纤维强度几乎完全丧失.

Before and after oxidizing,the microstructures and properties of two typical continuous SiC fibers sintered at different temperature were systematically studied by SEM,TEM and XRD.It is found that the grain size gradually decreases from the surface to the core of the F-1 fiber sintered at high temperature,but the content of graphite phase increases slightly.The F-2 fiber sintered at low temperature is mainly composed of amorphous SiCO phase,which contains a great deal of nanometer SiC grains and graphite.The strength of the F-1 fibers is 1.74 GPa due to the holes,while the strength of dense F-2 fiber reaches 2.76 GPa.Both fibers are oxidized during heating in air at 1000℃,and the oxide layers become thicker and the strength decreases with the prolongation of time.Although the grain boundaries act as diffusion channels of the F-1 fiber,the strength retention rate can still reach 55%after 10 h oxidation.The high temperature oxidation resistance of the F-1 fiber sintered at low temperature is very low.After oxidizing for 10 h,the thickness of the F-2 fibers reaches up to 430 nm so that the strength is almost completely lost.