Thermal conductivity and hardness of three single-phase high-entropy metal diborides fabricated by borocarbothermal reduction and spark plasma sintering

Gild, Joshua; Wright, Andrew; Quiambao-Tomko, Kathleen; Qin, Mingde; Tomko, John A.; Hoque, Md Shafkat Bin; Braun, Jeffrey L.; Bloomfield, Blake; Martínez, D.; Harrington, Tyler; Vecchio, Kenneth S.; Hopkins, Patrick E.; Luo, Jian

doi:10.1016/j.ceramint.2019.11.186

Cited by 116 publications

(63 citation statements)

References 54 publications

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“…In 2016, Gild et al [8] first reported the synthesis of single-phase high-entropy diborides in AlB 2 -prototyped hexagonal structure, which represents the first highentropy boride (HEB) fabricated. Follow-up studies synthesized the high-entropy diborides from boro/ carbothermal reduction of metal oxides [19][20][21] or elemental precursors [22][23][24]. Only a limited number of studies explored the HEBs with other metal-toboron stoichiometric ratios in monoboride (MB) or hexaboride (MB 6 ) structures [9,10,25].…”

Section: Introduction mentioning

confidence: 99%

A new class of high-entropy M3B4 borides

et al. 2020

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A new class of high-entropy M3B4 borides of the Ta3B4-prototyped orthorhombic structure has been synthesized in the bulk form for the first time. Specimens with compositions of (V0.2Cr0.2Nb0.2Mo0.2Ta0.2)3B4 and (V0.2Cr0.2Nb0.2Ta0.2W0.2)3B4 were fabricated via reactive spark plasma sintering of high-energy-ball-milled elemental boron and metal precursors. The sintered specimens were ∼98.7% in relative densities with virtually no oxide contamination, albeit the presence of minor (4–5 vol%) secondary high-entropy M5B6 phases. Despite that Mo3B4 or W3B4 are not stable phase, 20% of Mo3B4 and W3B4 can be stabilized into the high-entropy M3B4 borides. Vickers hardness was measured to be 18.6 and 19.8 GPa at a standard load of 9.8 N. This work has further expanded the family of different structures of high-entropy ceramics reported to date.

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Section: Introduction mentioning

confidence: 99%

A new class of high-entropy M3B4 borides

et al. 2020

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“…In the last two to three years, high-entropy ceramics have become a major global research emphasis. Different series of high-entropy ceramics, such as silicides [2,3], oxides [1,4], nitrides [5], carbides [6][7][8][9], and borides [10][11][12][13] have been widely studied. The subject of high-entropy boride (HEB) and high-entropy carbide (HEC) ceramics are, so far, the most intensively researched.…”

Section: Introductionmentioning

confidence: 99%

Fine-grained dual-phase high-entropy ceramics derived from boro/carbothermal reduction

Luo

Guo

Plucknett

et al. 2020

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In the current work fine-grained dual-phase, high-entropy ceramics (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2-(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C with different phase ratios are prepared from powders synthesized via a boro/carbothermal reduction approach, by adjusting the content of B4C and C in the precursor powders. Phase compositions, densification, microstructure, and mechanical properties have been investigated. Due to the combination of pinning effect and the boro/carbothermal reduction approach, the average grain sizes (0.5–1.5 µm) of the dual-phase high-entropy ceramics, were much smaller as compared with previously reported values. The dual-phase high-entropy ceramics with 15 mol% boride phase exhibit the highest Vickers hardness (24.21 GPa) and fracture toughness (3.2 MPa•m1/2).

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“…Another interesting general observation of HECs is represented by their enhanced mechanical properties. The generally observed enhanced hardness from the RoM averages [44,48,50,54,56,59,61,63,64,66] may be explained through solid-solution strengthening. Castle et al also highlighted the importance of the activated slip systems affecting hardness and the relative easiness of activation and switching of dominant slip systems [61].…”

Section: Mechanical Propertiesmentioning

confidence: 95%

“…1). Although the initial work on high-entropy borides resulted in relatively low densities (~ 92%) due to significant oxide contamination from high-entropy ball milling, several subsequent studies quickly improved powder synthesis and fabrication methods that enhanced relative densities and properties [46,47,[49][50][51][52][53][54][55][56]. In 2018 and 2019, several groups [21,22,[57][58][59][60][61][62][63][64][65][66] also independently reported the fabrications of high-entropy carbides as another subclass of high-entropy UHTCs.…”

Section: Graphical Abstractmentioning

confidence: 99%

“…The high-entropy borides and carbides are being examined for their potential use as nextgeneration UHTCs [118,119]. These classes of materials have also shown increased mechanical properties [56,61,62,64,66] and oxidation resistance [48,63,120,121] Notably, a general property of HECs is represented by the increased hardness in comparison with the RoM averages, which have been reported for high-entropy borides [48,50,54,56], carbides [59,61,63,66], and silicides [44,45]. Further discussion can be found in the next section.…”

Section: Propertiesmentioning

confidence: 99%

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A step forward from high-entropy ceramics to compositionally complex ceramics: a new perspective

2020

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High-entropy ceramics (HECs) have quickly gained attention since 2015. To date, nearly all work has focused on five-component, equimolar compositions. This perspective article briefly reviews different families of HECs and selected properties. Following a couple of our most recent studies, we propose a step forward to expand HECs to Compositionally Complex ceramics (CCCs) to include medium-entropy and non-equimolar compositions. Using defective fluorite and ordered pyrochlore oxides as two primary examples, we further consider the complexities of aliovalent cations and anion vacancies as well as ordered structures with two cation sublattices.Better thermally-insulating yet stiff CCCs have been found in non-equimolar compositions with optimal amounts of oxygen vacancies and in ordered pyrochlores with substantial size disorder.It is demonstrated that medium-entropy ceramics (MECs) can prevail over their high-entropy counterparts. The diversifying classes of CCCs provide even more possibilities than HECs to tailor the composition, defects, disorder/order, and, consequently, various properties.

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Thermal conductivity and hardness of three single-phase high-entropy metal diborides fabricated by borocarbothermal reduction and spark plasma sintering

Cited by 116 publications

References 54 publications

A new class of high-entropy M3B4 borides

A new class of high-entropy M3B4 borides

Fine-grained dual-phase high-entropy ceramics derived from boro/carbothermal reduction

A step forward from high-entropy ceramics to compositionally complex ceramics: a new perspective

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