The role of Cr addition on the processing and mechanical properties of high entropy carbides

Due to the presence of core effects of high‐entropy materials, it is believed that the impact of carbon vacancy in high‐entropy carbides may differ from that of transition metal monocarbides. In this work, nonstoichiometric high‐entropy carbides (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C1−x (HEC1−x) with variable carbon vacancy concentration were fabricated by spark plasma sintering using powder mixtures of high‐entropy carbide and metallic powders. Compared with the corresponding monocarbides, the decline rates of lattice constant and elastic modulus were obviously slower as carbon vacancy concentration increased, indicating a more rigid crystalline lattice in the high‐entropy carbide. The valence electron number for HEC1−x ceramics with the highest hardness is 7.6, which is inconsistent with the theoretically predicted value of 8.4 for the traditional transition metal carbides. When the carbon vacancy concentration in HEC1−x ceramics is above 20%, the promoting effect of carbon vacancy on grain growth will outweigh the inhibiting effect of sluggish diffusion on grain growth, causing grains to grow quickly.

Section: Introductionmentioning

confidence: 99%

“…However, carbon vacancies still have substantial effects on the lattice parameter of MC 1−x . [1][2][3] For monocarbides consisting of IVB and VB metal elements, their lattice constants often decrease with the increase of the carbon vacancy concentration. For example, the lattice constant of TaC 0.7 is 1.3% lower than that of TaC 1.0 .…”

Section: Introductionmentioning

confidence: 99%

Lattice rigidity in high‐entropy carbide ceramics with carbon vacancies

Liu

Guo

et al. 2023

“…As a contrast, when the sintering temperature was raised to 2000°C, the segregation of Zr element in the Cr0‐2000 sample disappeared. Overall, the metallic elements within high‐entropy carbides exhibited some degree of solid solubility in CrN, 19 and the liquid phases were present during the sintering process, which facilitated the solution‐reprecipitation process of high‐entropy carbides and subsequently promoted the densification of HEC ceramics.…”

Section: Resultsmentioning

confidence: 99%

“…Overall, the metallic elements within high-entropy carbides exhibited some degree of solid solubility in CrN, 19 and the liquid phases were present during the sintering process, which facilitated the solution-reprecipitation process of high-entropy carbides and subsequently promoted the densification of HEC ceramics. Figure 4 shows the SEM morphologies of the polished and etched samples fabricated in this study.…”

Section: Density (G/cmmentioning

confidence: 99%

Low‐temperature sintered (Ti, Zr, Nb, Ta, Mo)C ceramics with improved hardness and toughness by using CrN as sintering additive

Liu,

Liang,

Guo

et al. 2024

Currently, previous studies of low‐temperature sintering of high‐entropy carbide ceramics (HECCs) have followed the traditional approach to use the low‐melting‐point metals, such as Co, Ni, and so forth, as sintering additives. However, metallic binders can cause adverse impacts on hardness of HECCs. This study reported an innovation processing method for low‐temperature sintering of HECCs, which involved the use of various contents of CrN as sintering additive and spark plasma sintering at 1600°C to obtain dense HECCs. In comparison to the grain size of pure (Ti, Zr, Nb, Ta, Mo)C bulk sintered at 2000°C (3.29 ± 1.02 μm), the grain size of samples with the addition of 5–15 wt.% CrN sintered at 1600°C was significantly smaller, ranging from 0.32 to 0.48 μm. By using only 5 wt.% CrN, dense (Ti, Zr, Nb, Ta, Mo)C ceramics with a high hardness value of 26.73 ± 0.43 GPa could be obtained. Furthermore, increasing the amount of CrN to 15 wt.% resulted in a fracture toughness of 3.78 ± 0.10 MPa·m1/2. It is anticipated that the (Ti, Zr, Nb, Ta, Mo)C ceramic with an ideally combined hardness and toughness can be achieved at low sintering temperatures by the proper control of CrN content.

“…34,38 Similarly, the addition of Cr increased the lattice distortion of HEC 5 -Cr ceramics, thereby improving its nano-hardness through solid solution strengthening effect. 25 In addition, Cr increased the random interactions between different elements, which may lead to the increase of Peierls stress for dislocation slip. 39 However, from Figure 4D, when WC content reaches 15 wt.%, W element shows obvious aggregation, which is usually unfavorable to the mechanical properties of ceramics.…”

Section: F I G U R Ementioning

confidence: 99%

Effect of WC content on microstructure and mechanical properties of (TiZrHfNbTaMo)C‐15 wt.% Co ceramics

Deng,

Kang,

Zhang

2024

The (TiZrHfNbTaMo)C‐15 wt.% Co ceramics with excellent comprehensive properties were successfully prepared by vacuum liquid phase sintering. The effects of WC content on the grain size, microstructure, and mechanical properties were investigated. The results showed that WC was dissolved into (TiZrHfNbTaMo)C phase to form a seven‐component solid solution, and the independent WC phase disappeared. The addition of WC improved the wettability between the ceramic phase and the metal phase and promoted the densification of the ceramics. In addition, WC played a role in refining grains and inhibiting the grains growth to a certain extent. The comprehensive properties of ceramics were improved by solid solution strengthening and high entropy effect. When the WC content was 5 wt.%, the toughness reached the maximum of 9.41 ± 0.15 MPa·m1/2, and the hardness of the ceramic with 10 wt.% WC achieved the highest value of 18.18 ± 0.20 GPa.