First-principles study, fabrication and characterization of (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramics

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The synthesis of high‐entropy metal carbide powders is critical for implementing their extensive applications. However, the one‐step synthesis of high‐entropy metal carbide powders is rarely studied. Herein, the synthesis possibility of high‐entropy metal carbide powders, namely (Zr0.25Ta0.25Nb0.25Ti0.25)C (ZTNTC), via one‐step carbothermal reduction was first investigated theoretically by analyzing chemical thermodynamics and lattice size difference based on the first‐principle calculations, and then the ZTNTC powders with particle size of 0.5‐2 μm were successfully synthesized experimentally. The as‐synthesized powders not only had a single rock‐salt crystal structure of metal carbides, but also possessed high‐compositional uniformity from nanoscale to microscale. More interestingly, they exhibited the distinguished coral‐like morphology with the hexagonal step surface, whose growth was governed by a classical screw dislocation growth mechanism.

“…Therefore, by using the energies from DFT calculations in Table , the

normalΔ H_{mix}^{0 normalK}

is calculated to be about −1.423 kJ/mol, as listed in Table , suggesting that ZTNTC is thermodynamically stable in terms of four individual metal carbides at 0 K and 0 Pa. Meanwhile, the

Δ S_{mix}

of ZTNTC can be expressed as follows:

\begin{matrix} normalΔ S_{mix} = - \frac{R}{2} 2.047em2.047emtrue[\sum_{i = 1}^{N_{k}} \begin{matrix}  \end{matrix} x_{i}^{k} \ln ()(, x_{i}^{k}) + x_{v}^{h} \ln ()(, x_{v}^{h}) \\ + (1 - x_{v}^{h}) \ln (1 - x_{v}^{h}) 2.047em2.047emtrue] \end{matrix}

where R is the ideal gas constant, N k is the element species in the metal sublattice,

x_{i}^{k}

is the molar fractions of the constituent i in the metal sublattice, and

x_{v}^{h}

is the molar fraction of the vacancies in the carbon sublattice. In the present work, we assume that there are no carbon vacancies and thereby the

Δ S_{mix}

of ZTNTC can be calculated to be 0.693 R (Table ).…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, an empirical parameter (

δ

δ = \sqrt{\sum_{i = 1}^{n} c_{i} {()(, 1 - \frac{r_{i}}{\overset{false¯}{r}})}^{2}}

\overset{false¯}{r} = {false\sum}_{i = 1}^{n} c_{i} r_{i}

. The calculated

δ

δ

suggests smaller lattice distortions in the solid solutions, which will promote the formation of the solid solutions.…”

Section: Resultsmentioning

confidence: 99%

One‐step synthesis of coral‐like high‐entropy metal carbide powders

Ning

Liu

et al. 2019

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“…A total of 20 indentations were conducted on each sample. A semi‐empirical fracture mechanics analysis of the cracks associated with microindentations yields a measure of fracture toughness, K IC (Equation ), given as:

K_{IC} = χ {()(, \frac{E}{H})}^{1 / 2} \frac{p}{c^{3 false/ 2}},

where p is the applied load (N); χ is an empirical constant, H is the hardness (GPa); E is the Young's modulus (GPa) and c represents the average crack length (m) determined from the four radial cracks produced from indentations.…”

Section: Experimental Methodsmentioning

confidence: 99%

Densification, strengthening and toughening in hafnium carbide with the addition of silicon carbonitride

Hao

Guo

et al. 2020

Hafnium carbide (HfC) possesses low toughness and damage tolerance, which limits its application as high‐temperature structural materials. Here we report a route to fabricate a dense HfC with high toughness by incorporating a two‐component SiCN (silicon carbonitride) sintering aid, which is composed of SiCN and turbostratic carbon in the spark plasma sintering. The addition of the SiCN not only enhances the density (up to ~97%) of the final product, but more importantly results in an increase in toughness from 4.3 to 8.5 MPa m1/2 with only a 10% reduction in the flexural strength. The improvement has been attributed to the unique microstructure of the obtained samples, exhibiting several important characteristics: (a) homogeneously dispersed SiCN and C secondary phases in the HfC matrix to control grain size; (b) HfC grains contain different levels of Si, O, and N to form solid solution; (c) enrichment of free carbon at grain boundaries and triple junctions.

“…Ultra‐high temperature ceramics (UHTCs), including transition‐metal carbides, borides, and nitrides, have recently been receiving great research attention for potential harsh environment applications in nuclear reactors, cutting tools, and aerospace, owing to their outstanding comprehensive high‐temperature physical and chemical properties . However, the existing UHTCs cannot meet the increased requirements with the rapid development of the next‐generation hypersonic flight vehicle and engine parts.…”

Section: Introductionmentioning

confidence: 99%

“…Among the existing solid‐solution ceramics, the solid‐solution ceramics of transition‐metal carbides, are regarded as the most ideal candidates for the extreme environment since their individual metal carbide components possess high melting point (>3000°C), outstanding high‐temperature stability, and good mechanical performance . Up to now, numerous methods have been developed to synthesize the solid‐solution ceramics of transition‐metal carbides, including reaction sintering, carbothermal reaction, arc melting, and polymer‐derived‐ceramic (PDC) route . Among those advanced fabrication methods, PDC route is considered as an ideal route to obtain ceramic matrix composites due to its advantage of polymer‐processing techniques .…”

Section: Introductionmentioning

confidence: 99%

Synthesis of the ternary metal carbide solid‐solution ceramics by polymer‐derived‐ceramic route

Liu

Chu

2020

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The polymer‐derived‐ceramic (PDC) route has been widely used to fabricate the transition‐metal carbides (TMCs). Previously reported works focused mainly on the synthesis of the single or binary TMCs, while the synthesis of the ternary or more component TMCs was rarely reported. Herein, a class of the ternary TMCs, namely (Nb1/3Zr1/3Ta1/3)C solid‐solution ceramics, was successfully synthesized via PDC route for the first time. The as‐synthesized ceramics exhibited the particle‐like morphology with an average particle size of ~250 nm and showed a single rock‐salt crystal structure of metal carbides. At the same time, they had high compositional uniformity from nanoscale to microscale. In addition, they possessed low‐oxygen impurity content of 0.79 wt% and moderate‐carbon impurity content of 8.98 wt%. Such work provides a novel route to fabricate the ternary or more component TMCs.