Gradient-damage failure mechanism and strength model calculation considering thickness damage factor of HfC-SiC multiphase matrix composites in ultra-high temperature environments

Abstract

HfC-SiC multiphase matrix composites were fabricated via CVI method and microstructure, gradient damage behavior, and fracture characteristics of the composites were systematically investigated under varying temperatures. Results indicated that the ablation behavior was governed by oxygen partial pressure and oxidation product dynamics, which disrupt the "Hf-Si-O self-healing effect" at the surface. Post-breakdown of the oxidation barrier, the ablation-induced damage evolved into a three-layered gradient mechanism gradient mechanism along the composites’ thickness: surface ablation-oxidation failure, intermediate oxidation-defect proliferation, and basal load-bearing failure. This degradation reduced bending strength from 386.5 MPa to 207.9 MPa. Then, a theoretical model integrating thickness-dependent damage factors and thermal residual stresses was established to predict ablation-induced thermal fracture strength under ultrahigh-temperature conditions. The model accurately predicts post-ablation mechanical strength across 2300 °C (292.4 MPa) to 2700 °C (207.9 MPa). This gradient damage-based strength model provides critical insights for composite design and material selection in extreme engineering applications.