Evolution of Pseudoplastic Crack Propagation Mechanism in C/Sic-Hfc Composites Induced by Sic Bearing Layer Thickness Change and Residual Stress Reduction

Abstract

In this work, C/SiC-HfC composites with different thicknesses of SiC layer (about 0, 0.5, 1.0, and 1.5 μm) were prepared by the combination process of chemical vapor infiltration and precursor impregnation pyrolysis. The bending failure process and ablation behavior of these composites were characterized and investigated. In addition, a pseudoplastic crack propagation model during the bending process was established based on the microstructure of the fracture. The stress intensity factor was used as a criterion. The propagation process of cracks in the matrix was determined. After preparing the SiC layer of 1.5 μm on the fiber surface, the linear ablation rate of C/SiC-HfC composites increased from 5.04 ± 0.24 to 8.25 ± 0.16 μm/s. Surprisingly, the bending strength of the composites increased from 115.13 ± 6.34 to 286.09 ± 17.56 MPa (an increase of 148%), due to the excellent mechanical properties of SiC and the consumption of crack propagation energy by type II cracks near the SiC-HfC interface. After ablation, the strength retention rate of C/SiC-HfC composites first increased and then decreased with the enhancement of SiC layer thickness (increased from 71.82% to 85.36%, then decreased to 66.75%). In addition, due to the release of residual stress inside the high-temperature environment of ablation, the pseudoplastic characteristics of C/SiC-HfC composites were enhanced. C/SiC-HfC composites exhibit a high strength retention rate after failure.

Keywords: C/SiC-HfC composites, ablation behavior, crack propagation, pseudoplastic, flexural strength