Enhanced oxygen blocking properties of HfB2-SiC coating by LaB6-HfB2 synergistic reinforcement

To enhance the oxygen blocking properties of HfB2-SiC coatings at high temperatures, LaB6-HfB2 synergistic reinforcement was used to prepare HfB2-SiC-LaB6 coatings, whose oxidation resistance mechanism as well as the structural evolution at 1700 degrees C was investigated. After LaB6 modification, part of La diffused into Hf-Si-O glass, forming a more stable Hf-La-Si-O composite glass layer. Refractory La oxides embedded in the glass layer, preventing crack propagation and effectively inhibiting the internal diffusion of oxygen. Compared to HfB2-SiC coating, 5 vol% LaB6 added HfB2-SiC coating exhibited the best oxygen blocking performance, whose oxygen permeability and carbon loss rate reduced by 85.3 % and 74.2 %, respectively. However, when LaB6 was added in excess, the excess La2O3 formed by the oxidation of LaB6 consumed local SiO2 in the glass layer, which disrupted the integrity of the glass layer and increased the diffusion of oxygen.