Actively-controlled PyC interphase failure mechanisms in C/SiC composite revealed using micro-mechanical interfacial testing

Pyrolytic carbon (PyC) interphase plays a crucial role in improving the toughness and strength in ceramic matrix composites (CMCs). In this work, a micromechanical testing method combining micropillar compression and half-fiber push-out was developed to investigate the interfacial properties and failure behavior of high-textured PyC (HT-PyC) and low-textured PyC (LT-PyC). C_f/PyC/SiC samples were fabricated using actively-controlled chemical vapor deposition (CVI). The test results, determined by the Mohr-Coulomb fracture criterion, revealed that the interfacial debonding shear strength (IDSS) and internal friction coefficients (IIFC) were 322 MPa and 0.139 for HT-PyC, and 163 MPa and 0.341 for LT-PyC, respectively. The design of micropillars and half-fiber samples enabled comprehensive observation of the fracture surfaces. The findings indicate that variations in the PyC microstructure significantly influence crack propagation, affecting interfacial mechanical properties. Randomly distributed pores and amorphous carbon in LT-PyC create weak pathways for crack propagation, resulting in a lower IDSS compared to HT-PyC. However, the zigzag fracture paths impede slip initiation, leading to a higher IIFC. Furthermore, the micromechanical test results correlated with the properties of mini-C_f/SiC composites, providing guidance for the design of interphases through texture modulation of PyC to meet performance requirements.