Exploration of the oxidation behavior and doping ratio of the Si–HfO2 bond layer used in environmental barrier coatings

Hafnia doping is expected to improve the performance of the silicon‐bond layer of environmental barrier coatings (EBCs) for SiC‐based ceramic matrix composites. The optimal doping ratio, distribution of HfO2, and oxidation mechanism of the bond layer have not yet been fully addressed. A prototype Si–HfO2 bond layer with a designed HfO2‐rich area was used to examine its oxidation behavior. A random dispersion model was developed to calculate the optimal HfO2 doping ratio and its appropriate distribution state. The simulation results recommended that 20–30 vol% is the optimal doping ratio, where HfO2 is well dispersed inside Si without forming networks. This enables HfO2 to react with and consume SiO2 without accelerating oxygen diffusion inside the bond layer. This was confirmed by oxidation experiments on Si–xHfO2 tablets, in which the thinnest thermally grown oxide was achieved for the 20 vol% HfO2‐doped Si tablet. Both the microstructure design and material composition selection are highly important to further boost the performance of the EBCs.