Effect of curvature radius on the oxidation protective ability of HfB₂-SiC-MoSi₂-Si/SiC-Si coating for C/C composites

To investigate the effect of shape features on the oxidation behavior of the coated carbon/carbon (C/C) composites, HfB₂-SiC-MoSi₂-Si/SiC-Si coatings were prepared on C/C composites with three different curvature radii (R) by pack cementation (PC) and slurry dipping (SD) combined with gaseous silicon infiltration (GSI). A coupled experimental and simulation approach was used to discuss their microstructure evolutions and oxidation behaviors. After oxidation at 1650 °C for 618 h and cooled to 1050 °C in 2 h, the mass loss was reduced by 57.9 % (from 6.23 % to 2.62 %) as the curvature radius increases from 5 mm to 9 mm. The erosion effect of Si on curved samples increases with the increase of curvature, resulting in severe coating thinning and poorer oxygen barrier for samples with smaller R compared to samples with larger R. The thermal stress during the oxidation cooling process is positively correlated with curvature, which promotes the initiation and propagation of cracks. Additionally, the composition uniformity of the coating decreases with the increase of curvature. All above reasons lead to the poor oxidation resistance of the samples with smaller R. This investigation provides insights for the service behavior of special-shaped components in high temperature oxygen-containing environment.