Ablation Behavior of High-temperature Laminated Ta/Ta0.5Hf0.5C Cermets under High-frequency Plasma Wind Tunnel Test

Laminated Ta/Ta0.5Hf0.5C cermets, characterized by high strength, high toughness, and high-temperature resistance, are excellent candidate materials for structural applications in aerospace field. To further investigate ablation performance of Ta/Ta0.5Hf0.5C cermets under high-temperature environment, a high-frequency plasma wind tunnel was utilized to evaluate their ablation resistance at nearly 3000 degrees C. Their phase composition and microstructure before and after ablation were characterized and analyzed. Results revealed that the laminated Ta/Ta0.5Hf0.5C cermets demonstrated remarkable ablation resistance, with a mass ablation rate of 0.061 g/s and a linear ablation rate of 0.019 mm/s. During the ablation process, distinctive ridge-groove surface morphologies and internal cracks were produced along the layered structure direction. These features were attributed to inconsistent ablation rates and thermal expansion coefficients of Ta metal layer and Ta0.5Hf0.5C ceramic layer. Specifically, the ridge region primarily consisted of Hf6Ta2O17 formed by oxidation of Ta0.5Hf0.5C ceramic layer. This compound could stably exist at high temperatures to protect the interior of ceramic layer from further oxidation. In contrast, the groove region primarily comprised Ta2O5, which was formed by oxidation of Ta metal layer. Yet Ta2O5 had a tendency to melt and vaporize at elevated temperatures, potentially leading to ejection or loss toward the ablation edge. The cracks formed within the layered structure during cooling process after ablation were mainly generated by thermal stress acting on the Ta0.5Hf0.5C ceramic layer due to differences in thermal expansion coefficients between the layers. Additionally, the Ta2C interfaces between metal and ceramic layers played a crucial role in branching, deflecting, and initiating micro-cracks, which endowed the material with good thermal shock resistance.