Two‐step synthesis process for high‐entropy diboride powders

Li, Feng; Fahrenholtz, William G.

doi:10.1111/jace.16801

Cited by 73 publications

(52 citation statements)

References 28 publications

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“…Unlike HEAs with only a single lattice structure occupied by metal elements, HECs possess two different sublattice structures, namely a cationic sublattice structure and an anionic sublattice structure occupied by metallic or nonmetallic elements, respectively. To date, a variety of HECs with only multi‐cationic sublattice structure, including metal oxides, 2,3 carbides, 4‐11 and diborides, 12‐15 with some superior physical and chemical performances, such as high hardness, low thermal conductivity, good corrosion resistance, and superior electrochemical properties, have been successfully explored. However, it is well known that the combined disorder of the cationic and anionic sites in HECs can produce much more unique physical and chemical characteristics compared with HECs with only multi‐cationic sublattice structure, which is expected to promote or expand HEC's potential applications in the functional, structural and other fields.…”

Section: Introductionmentioning

confidence: 99%

Thermophysical and mechanical properties of novel high‐entropy metal nitride‐carbides

Wen

Nguyen

et al. 2020

J Am Ceram Soc

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In this work, a novel (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)(N0.5C0.5) high‐entropy nitride‐carbide (HENC‐1) with multi‐cationic and ‐anionic sublattice structure was reported and their thermophysical and mechanical properties were studied for the first time. The results of the first‐principles calculations showed that HENC‐1 had the highest mixing entropy of 1.151R, which resulted in the lowest Gibbs free energy above 600 K among HENC‐1, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)N high‐entropy nitrides (HEN‐1), and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy carbides (HEC‐1). In this case, HENC‐1 samples were successfully fabricated by hot‐pressing sintering technique at the lowest temperature (1773 K) among HENC‐1, HEN‐1 and HEC‐1 samples. The as‐fabricated HENC‐1 samples showed a single rock‐salt structure of metal nitride‐carbides and high compositional uniformity. Meanwhile, they exhibited high microhardness of 19.5 ± 0.3 GPa at an applied load of 9.8 N and nanohardness of 33.4 ± 0.5 GPa and simultaneously possessed a high bulk modulus of 258 GPa, Young's modulus of 429 GPa, shear modulus of 176 GPa, and elastic modulus of 572 ± 7 GPa. Their hardness and modulus are the highest among HENC‐1, HEN‐1 and HEC‐1 samples, which could be attributed to the presence of mass disorder and lattice distortion from the multi‐anionic sublattice structure and small grain in HENC‐1 samples. In addition, the thermal conductivity of HENC‐1 samples was significantly lower than the average value from the “rule of mixture” between HEC‐1 and HEN‐1 samples in the range of 300‐800 K, which was due to the presence of lattice distortion from the multi‐anionic sublattice structure in HENC‐1 samples.

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Section: Introductionmentioning

confidence: 99%

Thermophysical and mechanical properties of novel high‐entropy metal nitride‐carbides

Wen

Nguyen

et al. 2020

J Am Ceram Soc

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“…These include several solid solutions of binary metal borides such as (Hf,Zr)B 2 resulting in a broadening of the primary HEB peaks, with a tail on the low-2θ side, as well as cubic TaC. Reports on the BCTR synthesis of HEBs have also shown secondary phase formation, including binary borides, at lower annealing temperature [6,18]. In contrast, the sample processed at 2000 • C has much sharper HEB peaks, with only very minor secondary phases, indexed primarily to excess B 4 C that was used in the precursor mixture.…”

Section: Resultsmentioning

confidence: 99%

“…Appropriate amounts of the precursor powders were chosen, with stoichiometry being calculated from the metal basis in an attempt to produce an equimolar diboride given as: (Hf 0.2 , Zr 0.2 , Ti 0.2, Ta 0.2, Mo 0.2 )B 2 . As is typically reported for BCTR [6,18], an excess of B 4 C was added to compensate for the loss of B due to evaporation of volatile boron oxide species during synthesis. Precursor powders were milled using a high energy ball mill (Spex 8000 M, Metuchen, NJ, USA) with a tungsten carbide (WC)lined cylindrical sample vial of 2.25 inch diameter and 2.5 inch length.…”

Section: Methodsmentioning

confidence: 99%

Single-Step Synthesis Process for High-Entropy Transition Metal Boride Powders Using Microwave Plasma

et al. 2021

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A novel approach is demonstrated for the synthesis of the high entropy transition metal boride (Ta, Mo, Hf, Zr, Ti)B2 using a single heating step enabled by microwave-induced plasma. The argon-rich plasma allows rapid boro-carbothermal reduction of a consolidated powder mixture containing the five metal oxides, blended with graphite and boron carbide (B4C) as reducing agents. For plasma exposure as low as 1800 °C for 1 h, a single-phase hexagonal AlB2-type structure forms, with an average particle size of 165 nm and with uniform distribution of the five metal cations in the microstructure. In contrast to primarily convection-based (e.g., vacuum furnace) methods that typically require a thermal reduction step followed by conversion to the single high-entropy phase at elevated temperature, the microwave approach enables rapid heating rates and reduced processing time in a single heating step. The high-entropy phase purity improves significantly with the increasing of the ball milling time of the oxide precursors from two to eight hours. However, further improvement in phase purity was not observed as a result of increasing the microwave processing temperature from 1800 to 2000 °C (for fixed ball milling time). The benefits of microwave plasma heating, in terms of allowing the combination of boro-carbothermal reduction and high entropy single-phase formation in a single heating step, are expected to accelerate progress in the field of high entropy ceramic materials.

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“…Usually, a small amount of B 2 O 3 is found on the surface of B 4 C, which has a higher vapor pressure at high temperature. Additionally, influence of O 2 impurity in Argon as well as diffused through the corundum furnace tube on the amount of B 4 C cannot be ignored [13]. On the other hand, Qin [24] et al found the dissolution and stability of soft WB 2 phase in high-entropy ceramics, the formation of (W x , M 1-x )B solid solution phase could be explained via the formation enthalpies between AlB 2 -type and CrB-type structures.…”

Section: Preparation Of Heb Powdersmentioning

confidence: 99%

“…In recent years, many methods have been successfully used to prepared the high-entropy borides, including the direct synthesis by high-temperature treatment using metal diboride powders as raw materials [1,6], the borothermal reduction method [7] and boro/carbothermal reduction method from oxides materials [8][9][10][11][12][13][14], and self-propagating hightemperature synthesis from metal and B powders [15], molten salt synthesis method [16] and so on. Among these methods, the boro/carbothermal reduction method can realize the large-scale production of high entropy diboride powders, which has been verified in preparing single phase diboride powders [17,18].…”

Section: Introductionmentioning

confidence: 99%

Synthesis of high-entropy boride powders via boro/carbothermal reduction method

Yang

Gong

Song

et al. 2021

Journal of Asian Ceramic Societies

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In this paper, high-purity and fine (W 0.2 V 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 (HEB) powders were obtained via a simple high-energy ball milling-assisted boro/carbothermal reduction method at 1600°C. Results showed that the heating temperature and B source contents played a key role in the synthesis of purity of single-phase HEB powders. When excess 10 wt.% B 4 C was introduced, the single-phase HEB powders were synthesized at 1600°C, and its grain size was ~150 nm and it showed the hexagonal crystal structure of metal diborides. EDS results showed the high compositional uniformity of W, V, Ta, Nb, Ti and B elements in HEB powders. Through discussing the thermodynamics process related to these possible chemical reactions and combining the XRD results at different temperatures, it was obtained that higher temperature and enough B source were required to stimulate the formation of high-entropy phase. This work will be a vital step for the commercialization of high-entropy boride powders.

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Two‐step synthesis process for high‐entropy diboride powders

Cited by 73 publications

References 28 publications

Thermophysical and mechanical properties of novel high‐entropy metal nitride‐carbides

Thermophysical and mechanical properties of novel high‐entropy metal nitride‐carbides

Single-Step Synthesis Process for High-Entropy Transition Metal Boride Powders Using Microwave Plasma

Synthesis of high-entropy boride powders via boro/carbothermal reduction method

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