Carbon fiber surface modification for tailored fiber-matrix adhesion in the manufacture of C/C-SiC composites

The surface of a commercial PAN-based carbon fiber (CF) was modified to optimize fiber–matrix adhesion (FMA) in a CF-reinforced polymer (CFRP) preform used for the manufacture of CF-reinforced silicon carbide (C/C-SiC) composites. For these purposes, CFs were thermally desized and then electrochemically oxidized. The surface of the fibers was investigated by atomic-force microscopy. The CFs’ chemical composition, specific surface acidity and wettability were investigated by different analytical methods. CFRPs based on electrochemically oxidized and untreated CFs were subsequently carbonized and transformed into C/C-SiC via liquid silicon infiltration (LSI). The microstructure of the composites was investigated by scanning electron microscopy (SEM). Single-fiber push-out tests were used to characterize FMA and revealed the highest interfacial fracture toughness for the CFRP based on electrochemically oxidized CFs. The surface treatment also showed positive effects after siliconization, e.g., a lower conversion rate of the CFs and improved mechanical properties.