含铍碳化硅纤维的力学性能及其表面形貌研究

目的提高碳化硅纤维的高温力学性能。方法以含铍聚碳硅烷为原料,采用先驱体转化法制备含铍碳化硅纤维,对含铍碳化硅纤维进行SEM和XRD分析,并对其常温和高温力学性能进行测试。结果制得的纤维直径在20~30μm,表面光滑,无明显缺陷。纤维常温拉伸强度为600~700 MPa,与商品级碳化硅纤维有较大差距,但在空气中800℃加热2 h后,拉伸强度提升30%以上。在空气中1100℃加热2 h后,纤维表面形貌无明显改变,拉伸强度仍能保持90%以上。在空气中1200℃加热2 h后,纤维表面出现裂纹,导致其拉伸强度明显下降。普通Si C纤维的拉伸强度随着空气热处理温度的升高而不断下降,并且在相同的空气热处理温度下,其强度保留率明显低于含铍碳化硅纤维。在空气热处理过程中,含铍碳化硅纤维表面生成了Si O2层,而普通碳化硅纤维却没有生成Si O2。结论含铍碳化硅纤维在空气中具有优异的耐高温性能,原因是Be元素促使纤维表面的Si C氧化生成了Si O2保护层,一方面阻止了纤维内部材料被进一步氧化,另一方面对纤维表面起到了加强作用。

Mechanical Properties and Surface Morphology of SiC Fibers Containing Beryllium

ABSTRACT:Objective To improve the mechanical properties of SiC fibers. Methods PBeCS was used as the precursor, and SiC fibers containing beryllium were produced by polymer-derived method. SEM, XRD and tensile strength tests were carried out. Results SiC fibers containing beryllium had a diameter between 20 to 30μm, and their surface was smooth. With a tensile strength of 600~700 MPa, the fibers were not as good as the current commercial SiC fibers, however, after being treated under 800 ℃ for 2 h in the air, SiC fibers containing beryllium had an increase of over 30% on tensile strength, and without obvious changes in sur-face morphology. These fibers kept more than 90% strength after being treated at 1100 ℃ for 2 h in the air. However, after being treated at 1200 ℃ for 2 h in the air, cracks appeared on the surface of the fibers, along with a sharp decrease of tensile strength. When the temperature of heat treating rose, the tensile strength of ordinary SiC fibers kept decreasing which was always lower than that of SiC fibers containing beryllium. During the heat treatment in the air, a SiO2 layer appeared on the surface of Be-SiC fibers, but not on the surface of ordinary SiC fibers. Conclusion The reason for good mechanical properties of SiC fibers containing berylli-um under high temperature in the air may be that beryllium caused the oxidation of SiC to generate SiO2 on the surface of fibers, which prohibited inner materials from being oxidized, and meanwhile strengthened the surface of the fibers.