Nano-healing mechanism of surface flaws on high strength carbon fibers with high-temperature vapor deposition polymerization polyimide coatings

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The effect of polyimide coatings on the filament tensile strength of high strength polyacrylonitrile-based carbon fiber was studied by using a high-temperature vapor deposition polymerization(VDP) coating processes. We found that this coating has a positive impact on those fibers with artificial notches less than 30 nm in depth and the potential to heal nano-ordered surface flaws(nano-flaws) of the fibers, resulting in a 25% increase of the filament tensile strength. The formation of a high-dense phase and a weak interface near a fiber surface seem to contribute to increase the filament tensile strength as well as efficient infiltration of the VDP coating into nano-flaws.