Enhance mechanical properties and ablation resistance of high-entropy (Hf_0.25Zr_0.25Ti_0.25Ta_0.25)C ceramics by introducing W metal

Catastrophic brittleness hinders the application of high-entropy carbides as a thermal protection system in the ultra-high temperature ablation environments. This study investigated the microstructure, phase constitution, mechanical properties and ablation resistance of (Hf_0.25Zr_0.25Ti_0.25Ta_0.25)C high-entropy carbides modified by W with different contents. The fracture toughness of the sample modified with 40 mol% W reaches 3.17 MPa m^1/2compared to 2.91 MPa m^1/2from the W-free reference. After 30 s ablation under an oxyacetylene torch (2.4 MW/m²), the linear and mass ablation rates are −0.53 μm/s and −0.64 mg/s respectively, which are better than 7.37 μm/s and −0.61 mg/s from the W-free sample. In general, the content of W will influence the phase composition and the Ta₂O₅-WO₃ binary oxide system. A WC second phase can enhance the fracture toughness and assist with the self-healing of oxide layer, finally improving the mechanical properties and ablation resistance together. This work provides an alternative method to design tough high-entropy ceramics with superior toughness for extreme environments.