To enhance the service life of C/C composites under high-temperature gas erosion at 2600 °C , a Hf x Si y C z (x, y, z = 0–1) ceramic modification was applied using a hafnium-silicon alloy. The modified composite (HSCC) exhibits unique morphology and microstructure resulting from reactions between carbon and the alloy. From a thermodynamic perspective, the formation of HfC is preferential in the products. In addition, as the vacuum level increases, the Si content rises. With increasing molar ratio of carbon to Hf-Si alloy, the number of Hf x Si y C z ceramic grains increases, accompanied by a transition from micron to nanoscale grain size. TEM analysis of FIB sectioned HfC ceramics revealed that synthesized HfC particles contain embedded nanoscale Hf x Si y particles, within which elemental Si was detected. These findings confirm in-situ Si formation and support a mechanism whereby carbon atoms diffuse into the alloy to form carbides. After exposure to 2600 °C air plasma for 110 s, HSCC demonstrates outstanding ablation resistance, retaining an intact oxide layer and exhibiting a linear ablation rate as low as –5.2 μm/s. The ablation process triggers local mutual dissolution and interfacial reactions between HfO 2 and SiO 2 , leading to the formation of a compositionally graded Hf-Si-O amorphous transition layer. This reflects interdiffusion and structural integration of the oxides under extreme thermal conditions, rather than their independent growth. This study offers valuable insights for the design and application of in-situ ceramic-modified C/C composites in extremely high-temperature erosive environments.
Liu et al. (Fri,) studied this question.