Regulating thermochemical erosion to achieve high-cleanliness surfaces on C/SiC composites: Mechanisms of gas-medium assisted electric arc machining

Machining of carbon fiber-reinforced silicon carbide (C/SiC) composites typically causes severe physical damage and thermochemical degradation, thereby limiting surface quality and machining performance. This study develops a gas-medium-controlled electric arc machining (EAM) method to control the thermochemical erosion of C/SiC composites. In situ arc observation and multi-scale characterization unraveled the coupling of physical ablation and gas-mediated chemical erosion. An oxidizing atmosphere (air) favored intense exothermic reactions, which resulted in a high material removal rate but also in a thick Si–O-rich recast layer (≈200 μm), random local over-erosion, and severe Cu contamination (≈22 wt.%). Nitrogen medium induced Si–N-containing surface bonding, accompanied by thermal cracking and deposition of electrode material. On the contrary, argon showed the highest cumulative effective discharge energy (≈13.2 kJ in 30 s), which was 53.1% and 35.3% higher than those of air and nitrogen, respectively. It exhibited a stable discharge process that suppressed local over-erosion. Argon changed the material removal mechanism to stable physical ablation and sublimation by suppressing oxidation and electrode-material transfer, thus maintaining carbon-fiber integrity and reducing subsurface damage. Such results indicate that argon-assisted EAM is a promising approach for high-integrity machining of advanced ceramic matrix composites.