Effect of cryogenic thermal cycling on SiC-modified C/C composites

The bonding strength, mechanical properties and high-temperature thermal shock resistance of C/C–SiC composites after undergoing simulated low earth orbit environment including cryogenic thermal cycles (CTCs) between 153 and 393 K for 200 times with high-vacuum state of 1.3 × 10⁻³ Pa were investigated. Results of the tests showed that, the bonding strength at coating/substrate interface monotonically decreased as the CTCs increased. After 100 CTCs, the flexural strength of C/C–SiC composites enhanced and the percentage of remaining strength was 102.60%, while, the mass loss of specimens decreased from 2.08 to 0.89% after thermal shock resistance test between 1773 K and room temperature for 15 times. Once CTCs exceed 100 times, the mass loss increased, the flexural strength reduced and remained only 87.40% of initial strength after 200 CTCs. The fractural behaviour of CTCs-treated modified composites exhibited typical brittle mode. A model based on the evolution of the residual thermal stress after CTCs treatment was proposed to explain the oxidation failure mechanism of C/C–SiC specimens.