Nb- and Ta-doped (Hf,Zr,Ti)C multicomponent carbides with enhanced oxidation resistance at 2500 °C

Enhancing oxidation resistance of multicomponent carbides above 2000 ℃ is critical for their thermal protection applications. For this purpose, novel Nb- and Ta-doped (Hf,Zr,Ti)C multicomponent carbides were designed to improve their oxidation resistance at 2500 ℃. The results demonstrated that Nb and Ta doping reduced the oxidation rate constant by 16.67% and 25.17%, respectively, thereby significantly improving the oxidation resistance of (Hf,Zr,Ti)C. This enhancement was attributed to the changes in oxycarbide composition and distribution within the oxide layer by adding Nb and Ta. Owing to the different oxidation tendencies of the constituent elements, a distinctive structure was formed in which (Hf,Zr)O2 served as a skeleton, and various oxycarbides were dispersed throughout the oxide layer. The doped Nb and Ta were retained within oxycarbides, retarding the diffusion of oxygen into the lattice. More importantly, the addition of Nb and Ta reduced the size of oxycarbides, decreasing both size and quantity of the pores in the oxide layer and facilitating the formation of a more effective oxygen barrier.