Ablation behaviour of (Hf-Ta-Zr-Nb)C high entropy carbide ceramic at temperatures above 2100 °C

Abstract

The ablation behaviour of (Hf-Ta-Zr-Nb)C high entropy carbide (HEC4) was studied at temperatures above 2100 °C using a plasma flame gun in air. The microstructures, phase and chemical compositions of the HEC4 samples were investigated after ablation. The mass ablation rate of the HEC4 samples increased with increasing ablation time from 0.21 mg cm−2 s−1 for 60 s to 0.45 mg cm−2 s−1 for 120 s. Compared to the mono- and binary carbides with commonly decreased mass and thickness after ablation, the HEC4 samples with the increased mass and thickness after ablation showed good resistance to mechanical scouring at such high temperatures and an oxidation controlled ablation mechanism. The ablation processes mainly include the oxidation of the carbide, the phase separation of the oxides, the melting of oxides, and the diffusion of oxygen. A composition gradient in the oxide layer was detected due to the different melting temperatures of the different oxides; Nb-Ta rich oxides formed at the front surface melted and became enriched at the edge of the samples, and the Zr-Hf rich oxides were enriched in the centre of the samples. The oxide layer with complex compositions and phase distributions acted as an effective ablation barrier.