Microstructural investigation of dual-phase boride/carbide high-entropy ceramics

Abstract

Reactive sintered (Ti-Zr-Nb-Ta-Hf)B2 - (Ti-Zr-Nb-Ta-Hf)C dual-phase, high-entropy ceramics were prepared via a two-step spark plasma sintering (SPS) process at a maximum temperature of 2100°C, with a sintering time of 5 minutes at an applied pressure of 70 MPa. Microstructure analyses revealed no structural defects in the form of large pores, microcracks, or large grain clusters. The composite shows high relative density (~ 99%), and relatively homogeneous microstructure with average grain sizes of the boride and carbide phases 3 μm and 2 μm, respectively, with a negligible oxide content (HfO2/ZrO2 < 1wt%). It was found that Ti, Zr, and Nb elements are predominantly enriched in the boride phase, whereas Ta and Hf are concentrated more in the carbide phase.