Exploration of the oxidation behavior and doping ratio of the Si–HfO <sub>2</sub> bond layer used in environmental barrier coatings
Shikang Xiao, Jianzhang Li, Xinran Liu, Zixuan Chang, Panxin Huang, Antong Zhang, Yuhang Tian, Xu Zhang, Jingde Zhang, Guifang Han
Abstract
Abstract 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 HfO 2 , and oxidation mechanism of the bond layer have not yet been fully addressed. A prototype Si–HfO 2 bond layer with a designed HfO 2 ‐rich area was used to examine its oxidation behavior. A random dispersion model was developed to calculate the optimal HfO 2 doping ratio and its appropriate distribution state. The simulation results recommended that 20–30 vol% is the optimal doping ratio, where HfO 2 is well dispersed inside Si without forming networks. This enables HfO 2 to react with and consume SiO 2 without accelerating oxygen diffusion inside the bond layer. This was confirmed by oxidation experiments on Si– x HfO 2 tablets, in which the thinnest thermally grown oxide was achieved for the 20 vol% HfO 2 ‐doped Si tablet. Both the microstructure design and material composition selection are highly important to further boost the performance of the EBCs.