Synthesis, mechanical, and thermophysical properties of high‐entropy (Zr,Ti,Nb,Ta,Hf)C_0.8 ceramic

Abstract

Two high‐entropy carbides, including stoichiometric (Zr,Ti,Nb,Ta,Hf)C and nonstoichiometric (Zr,Ti,Nb,Ta,Hf)C0.8, were prepared from monocarbides and ZrH2. Their sinterability, microstructures, mechanical properties, thermophysical properties, and oxidation behaviors were systematically compared. With the introduction of carbon vacancy, the sintering temperature was lowered up to 300°C, Vickers hardness was almost unaffected, whereas the strength decreased significantly generally due to the decrease of covalent bonds. The thermal conductivity shows a 50% decrease for nonstoichiometry high‐entropy carbide, which is a major consequence of the lower electrical conductivity. The oxidation resistance in high temperature water vapor was not sensitive to carbon stoichiometry.

In situ reaction synthesis of high‐entropy carbide/diboride composite with high mechanical properties

“…For HEC‐3, the amount of residue carbon becomes further smaller, and oxides secondary phase can only be occasionally discovered. The decrease of the oxides secondary phase can be ascribed to the increased amount of ZrH 2 in the raw materials, which is in good accordance with the result in (ZrTiNbTaHf)C 0.8 34 . The gradual disappearance of residue carbon is a consequence of increased carbon vacancies which made the free carbon reenter the lattice of HEC 1‐δ .…”

“…The decrease of the oxides secondary phase can be ascribed to the increased amount of ZrH 2 in the raw materials, which is in good accordance with the result in (ZrTiNbTaHf)C 0.8 . 34 The gradual disappearance of residue carbon is a consequence of increased carbon vacancies which made the free carbon reenter the lattice of HEC 1-δ . Although the metal elements in (ZrTiNbTaHf)B 2 are homogeneously distributed, they are not equiatomic.…”

“…It has been demonstrated that carbon vacancies can significantly deteriorate the flexural strength of high-entropy carbides due to the weakened covalent bonding. 31,34 Besides, the weak interface bonding of HEC and residual carbon further decreases the flexural strength. HEC-0 shows a fracture toughness of 3.6 MPa*m 1/2 .…”

“…reported a constant decrease of flexural strength with increasing carbon vacancy in high‐entropy (TiZrHfVNbTa)C x 31 . In our recent study, it was demonstrated that the flexural strength of (TiZrHfNbTa)C 0.8 is only 1/3 of that for (TiZrHfNbTa)C 34 …”

“…26,31 Zhang et al reported a constant decrease of flexural strength with increasing carbon vacancy in high-entropy (TiZrHfVNbTa)C x . 31 In our recent study, it was demonstrated that the flexural 3 8.96 g/cm 3 9.01 g/cm 3 9.05 g/cm 3 strength of (TiZrHfNbTa)C 0.8 is only 1/3 of that for (TiZrHfNbTa)C. 34 Therefore, it is of great importance to enhance the mechanical properties of the non-stoichiometry HECs. In this study, we propose a novel routine which is highly promising to simultaneously lower the synthesis temperature and enhance the mechanical properties of HECs.…”