High-entropy carbide-nitrides with enhanced toughness and sinterability

Abstract

High-entropy ceramics (HECs) have attracted much attention due to their huge composition space, unique microstructure, and desirable properties. In contrast to previous studies, which have primarily focused on HECs with one anion, herein, we report a new family of ceramics with both multi-cationic and -anionic structures, i.e., high-entropy carbide-nitrides (Ti0.33Zr0.33Hf0.33)(C0.5N0.5), (Ti0.25Zr0.25Hf0.25Nb0.25)(C0.5N0.5) and (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)(C0.5N0.5). These as-synthesized HECs are mainly comprised of a face-centered cubic solid-solution phase accompanied by minor inevitable oxide phases. The formation mechanism of the solid-solution phase is discussed in terms of the lattice size difference and thermodynamic competition between configurational entropy and mixing enthalpy. It is found that the increment in the configurational entropy can effectively lower the sintering temperature and increase the fracture toughness. Particularly, the newly developed (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)(C0.5N0.5) exhibits a decent fracture toughness of 8.4 MPa m1/2 and a low sintering temperature of 1750°C, making it promising for ultra-high temperature applications. Our work not only enriches knowledge regarding the HECs categories, but also opens a new pathway for developing HECs with multi-cationic and -anionic structures.