BN和BN/SiC涂层对SiC纤维单丝拉伸性能的影响及其失效行为

Effect of BN and BN/SiC coatings on tensile properties and failure behavior of SiC fiber monofilament

采用化学气相渗透(CVI)工艺在两种国产典型SiC纤维表面沉积了BN和BN/SiC涂层,并对涂层的成分进行分析。利用Weibull分布评价SiC纤维的单丝拉伸强度,研究了沉积涂层前后纤维的拉伸断裂失效行为。结果表明,合适厚度(15 nm)的富碳层能够弥合SiC纤维表面的缺陷,减少纤维从表面开始失效的可能。采用CVI工艺制备的涂层厚度均匀,成分稳定;沉积BN和BN/SiC涂层后,两种SiC纤维的拉伸强度和弹性模量下降。BN涂层亦可修复纤维的表面缺陷,使纤维强度分布趋于集中。与无涂层纤维不同的是,沉积涂层后纤维拉伸断裂失效源分别为BN和SiC涂层的表面缺陷。

BN and BN/SiC coatings were deposited on the surface of two typical domestic SiC fibers by CVI process,and the composition of coatings was analyzed.The tensile strength of monofilaments was evaluated by Weibull distribution,and the tensile fracture failure behaviors of the fiber before and after depositing coatings were studied.The results show that the carbon-rich layer with appropriate thickness(15 nm)can heal the defects on the surface of SiC fiber and reduce the possibility of fiber failure from the surface.The thickness of the coating prepared by the CVI process is uniform and the composition is stable.After depositing BN and BN/SiC coatings,the tensile strength and elastic modulus of the two kinds of SiC fibers are decreased.BN coatings can also repair the surface defects of the fiber,so that the fiber strength distribution tends to be concentrated.Different from the uncoated fibers,the tensile fracture failure sources of coated fibers are the surface defects of BN and SiC coatings,respectively.