Tailoring an “outer ablation-resistant and inner oxygen-barrier” architecture in plasma-sprayed HfB2-SiC coatings: A novel strategy for stronger thermal protection ability

“Outer ablation-resistant and inner oxygen-barrier” architecture in HfB 2 -SiC coating. • Rapid solidification behavior during induction plasma spheroidization is revealed. • In situ DPV monitoring reveals stable in-flight behavior of HfB 2 -SiC droplets. • High-density HfB 2 -SiC coating resists 1900 °C ablation without spallation. Plasma sprayed HfB 2 -SiC ultrahigh-temperature ceramic (UHTC) coatings suffer from inherent defects and progressive formation of SiC-depleted layer during high-temperature oxidation, leading to spallation degradation above 1800 °C. To address these issues, we propose a novel strategy that synergistically integrates powder feedstock engineering and coating architecture design without introducing any modifying additives. On the one hand, we successfully fabricated a high-density coating with reduced porosity (12.56%) by combining induction plasma spheroidized (IPS) HfB 2 -SiC feedstock powders with advanced DPV-based in-flight particle diagnostics technology. On the other hand, we developed a novel “outer ablation-resistant and inner oxygen-barrier” architecture of coating system. A Si-rich transition layer, fabricated by slurry sintering and pack cementation, served as an internal silicon reservoir. Results showed that the IPS coating demonstrated enhanced ablation resistance at 1900 °C with significantly reduced mass ablation rate (−0.056 mg/s) and effectively avoided the typical spallation failure. Based on the structural integrity of the coating retained after ablation, the evolution of cracks at the bottom of the depleted layer was identified as a potential indicator for assessing the coating ablation behavior. The IPS coating suppressed the oxidation of HfB 2 at the bottom of the depleted layer and prevented bilayer cracking, maintaining superior structural integrity and thermal protection capability. Download: Download high-res image (259KB) Download: Download full-size image