Study on Correlation Between Composition and Resistivity of SiC Fibers and Regulation via Nitriding Modification

SiC fiber electrical performance depends on chemical composition and surface layers. This work uses resistivity testing, 29Si MAS NMR (Nuclear Magnetic Resonance), SEM-EDS (Scanning Electron Microscopy, Energy-dispersive X-ray Spectrometry), XPS (X-ray Photoelectron Spectroscopy) and AES (Auger Electron Spectroscopy) to quantify how free carbon and carbon-rich coatings govern the resistivity of KD-I/II/S/SA fibers. Ammonia high-temperature nitriding gradually removes conductive free carbon and forms Si-N insulating phases to produce KD-SN1/2/3 fibers, enabling resistivity tuning across 10−1–108 Ω cm. Surface carbon thickness and bulk free carbon content are the primary resistivity regulators. Nitridation constructs dense nitrogen-rich insulating surface layers to significantly improve fiber insulating performance. This study establishes a qualitative composition–surface–resistivity correlation framework, providing a clear mechanistic understanding and reliable guidance for the design and fabrication of multifunctional high-temperature SiC fibers.