Damage and self-healing mechanisms of 2D SiCf/SiC composites during high-temperature low-cycle fatigue in air: A combined in-situ acoustic emission and microscopy study

Abstract

The fatigue behavior and the corresponding damage mechanism under near-service environment are critical for the engineering applications of SiC_f/SiC composites. In this work, a combined in-situ acoustic emission (AE) and microscopy method was applied to investigate the high-temperature fatigue damage mechanisms above the tensile proportional limit stress of SiC_f/SiC composites. The fatigue damage modes at 1350 °C in air were identified and the AE signals could be effectively divided according to five types of damage events. Combined with the microstructure analysis, the damage and failure mechanisms of composites under different maximum stress levels were elucidated, which were dominated by the competition between matrix cracking and crack self-healing. When the maximum stress was low (100 MPa), the cracks in the chemical vapor infiltration (CVI) SiC matrix could be quickly healed at 1350 °C. The specimen achieved fatigue run-out (10⁵ cycles) without failure, and the retention rate of ultimate tensile strength (UTS) and failure strain were 76.8 % and 51.2 %, respectively. The decrease in UTS was attributed to interfacial sliding reduction and fiber grain coarsening. The decrease in failure strain was mainly ascribed to the irreversible damage caused by matrix cracking and interfacial sliding. When the maximum stress was high (120–140 MPa), the crack opening displacement for the CVI-SiC matrix was so large that cracks could not be healed, and the fatigue failure was controlled by fiber oxidation degradation. This work is of great significance for a deep understanding of the fatigue behavior of SiC_f/SiC composites under near-service environment.