Equiatomic 9-cation high-entropy carbide ceramics of the IVB, VB, and VIB groups and thermodynamic analysis of the sintering process

Abstract

The preparation of high-entropy (HE) ceramics with designed composition is essential for verifying the formability models and evaluating the properties of the ceramics. However, inevitable oxygen contamination in non-oxide ceramics will result in the formation of metal oxide impurity phases remaining in the specimen or even escaping from the specimen during the sintering process, making the elemental compositions of the HE phase deviated from the designed ones. In this work, the preparation and thermodynamic analysis during the processing of equiatomic 9-cation HE carbide (HEC9) ceramics of the IVB, VB, and VIB groups were studied focusing on the removing of the inevitable oxygen impurity existed in the starting carbide powders and the oxygen contamination during the powder mixing processing. The results demonstrate that densification by spark plasma sintering (SPS) by directly using the mixed powders of the corresponding single-component carbides will inhibit the oxygen-removing carbothermal reduction reactions, and most of the oxide impurities will remain in the sample as (Zr,Hf)O2 phase. Pretreatment of the mixed powders at high temperatures in vacuum will remove most part of the oxygen impurity but result in a remarkable escape of gaseous Cr owing to the oxygen-removing reaction between Cr3C2 and various oxide impurities. It is found that graphite addition enhances the oxygen-removing effect and simultaneously prevents the escape of gaseous Cr. On the other hand, although WC, VC, and Mo2C can also act as oxygen-removing agents, there is no metal-containing gaseous substance formation in the temperature range of this study. By using the heat-treated powders with added graphite, equiatomic HEC9 ceramics were successfully prepared by SPS.

ZrB2‐based solid solution ceramics and their mechanical and thermal properties

“…[38][39][40] In recent years, the development of high-entropy ceramics (HECs) has provided a good opportunity for improving the performances of ZrB 2 -based ceramics by designing multicomponent solid solutions at atomic level due to high entropy effect, lattice distortion effect, sluggish diffusion, and "cocktail" effect. [41][42][43] The enhanced hardness, [44][45][46] thermal, 47,48 oxidation, [49][50][51] corrosion, 52,53 and irradiation resistance 54,55 can be found in reported high-entropy carbides, 56,57 nitrides, 58,59 borides, [60][61][62] oxides, 63,64 or silicides. 65,66 However, open reports are mainly focused on the preparation and properties of HECs with an equimolar ratio.…”

Fabrication of multi-anionic high-entropy carbonitride ultra-high-temperature ceramics by a green and low-cost process with excellent mechanical properties

“…Thus, considerable interests in HEUHTCs have been triggered in the field of materials science. However, up to now, studies on the preparation and characterization of HEUHTCs are mainly focused on single-anion HEUHTCs including carbides J u s t A c c e p t e d 3 [12][13][14][15], borides [3,16,17], nitrides [18][19][20], and silicides [21][22][23][24]. Compared with the widely investigated single-anion HEUHTCs, multi-anionic HE carbonitride UHTCs have higher configuration entropy, wider performance regulation space, and better mechanical properties, which have ignited extensive attentions from researchers [25,26].…”

“…presents the Gibbs free energy as a function of temperature for reactions (4)-(13). Based on the principle of the lowest Gibbs free energy, at 1700 ℃, ∆G˂0, metal oxides can participate in the reaction to generate the corresponding carbides and nitrides, the sequence of the possible carbides and nitrides generated are NbC, NbN, TaC, TaN, TiN, TiC, ZrN, HfN, ZrC and HfC.…”

Ta(B, C, N) and (Ta, Mi)(B, C, N) (Mi = Nb, W) ceramics by high‐energy ball milling: processing and solution mechanisms

“…MiC and MiN whose hardness can be as high as 20 GPa are often used as superhard materials. Besides, some have the same crystal structure, such as face‐centered cubic (Fcc) and hexagonal close‐packed, which makes them mutually soluble to form solid solutions under certain conditions 1–5 . Refs.…”

“…Besides, some have the same crystal structure, such as face-centered cubic (Fcc) and hexagonal close-packed, which makes them mutually soluble to form solid solutions under certain conditions. [1][2][3][4][5] Refs. [6,7] have shown that Ti atoms occupy the lattice points of the Fcc crystal, and B, C, and N atoms occupy the octahedral sites.…”