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

CVIprocess,andthecompositionofcoatingswasanalyzed.Thetensilestrengthofmonofilamentswas evaluatedby Weibulldistribution,andthetensilefracturefailurebehaviorsofthefiberbeforeand afterdepositingcoatingswerestudied.Theresultsshowthatthecarbon-richlayer withappropriate thickness(15nm)canhealthedefectsonthesurfaceofSiCfiberandreducethepossibilityoffiber failurefromthesurface.ThethicknessofthecoatingpreparedbytheCVIprocessisuniformandthe compositionisstable.After depositing BN and BN/SiC coatings,thetensile strength and elastic modulusofthetwokindsofSiCfibersaredecreased.BNcoatingscanalsorepairthesurfacedefectsof thefiber,sothatthefiberstrengthdistributiontendstobeconcentrated.Differentfromtheuncoated fibers,thetensilefracturefailure sources ofcoatedfibers arethe surface defects of BN and SiC coatings,respectively.