Toward Inexpensive Superhard Materials: Tungsten Tetraboride-Based Solid Solutions

Mohammadi, Reza; Xie, Miao; Lech, Andrew T.; Turner, Christopher L.; Kavner, A.; Tolbert, Sarah H.; Kaner, Richard B.

doi:10.1021/ja308219r

Cited by 109 publications

(142 citation statements)

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“…The structure of this material has been debated for more than half a century, but the need for a definitive solution has increased dramatically in recent years with the discoveries that WB 4.2 is both superhard and can serve as the parent phase for a large family of solid solutions that are even harder (8,9,11). Although the crystal structure reported here contains some elements postulated previously-sites that are only partly occupied by tungsten, for example (14,16,17,21)-the structure presents previously unidentified elements as well.…”

Section: Discussionmentioning

confidence: 99%

“…As mentioned above, WB 4.2 is capable of hosting a wide range of solute atoms, and these solute atoms can have a profound effect on hardness, even at very low concentrations (9). Having an accurate model for WB 4.2 provides valuable insight toward understanding these phenomena and more directly predicting the means of manipulating the crystal chemistry of this compound.…”

Section: Discussionmentioning

confidence: 99%

“…By carefully tailoring a solid solution scheme, it may be possible to select specific guest atoms to replace only the fully occupied tungsten site, only the partially occupied site, or both. It may further be possible to introduce other metals or heteroatoms at the vacant 2(d) position, replacing the cuboctahedra with metal atoms or, conversely, enhancing the frequency and regularity with which they occur (9). Changes in the spatial distribution of boron cuboctahedra upon doping with metal heteroatoms could possibly be the basis for the extraordinary changes in hardness that can be achieved at doping levels of just a few percent.…”

Section: Discussionmentioning

confidence: 99%

“…More dramatically, it is like ReB 2 (2), capable of scratching natural diamond (11). We have, furthermore, previously shown that the hardness of this compound may be enhanced by the creation of solid solutions with other transition metals (9). However, to understand the underlying mechanisms for the hardness enhancements observed in WB 4 solid solutions, as well as to guide the design of new superhard borides with tailored mechanical properties, it is crucial to understand the crystal structure of this compound.…”

mentioning

confidence: 96%

“…This trend is at least partially driven by a need for greater efficiency in cutting tools compared with tungsten carbide (which is not superhard), as well as the shortcomings of the traditional superhard compounds-diamond (which is unusable for cutting ferrous materials) (5) and cubic boron nitride (which is very expensive to synthesize and difficult to shape) (6). Within the rapidly growing family of superhard borides, tungsten tetraboride (or WB 4 ) is of specific interest due to its excellent mechanical properties and its relatively lower cost compared with borides such as ReB 2 , OsB 2 , RuB 2 , and RhB 2 , which contain platinum group metals (3,(7)(8)(9)(10)(11). For instance, tungsten tetraboride demonstrates an extremely high indentation hardness of ∼43 GPa by the Vickers method (under an applied load of 0.49 N) (8) and ∼41.7 GPa by nanoindentation (maximum, at a penetration depth of 95.25 nm; Fig.…”

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Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Lech

Turner

Mohammadi

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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113

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Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten-often referred to as WB 4 and sometimes as W 1-x B 3 -is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961-a fact that severely limits our understanding of its structure-property relationships and has generated increasing controversy in the literature. Here, we present a new crystallographic model of this compound based on refinement against time-of-flight neutron diffraction data. Contrary to previous X-ray-only structural refinements, there is strong evidence for the presence of interstitial arrangements of boron atoms and polyhedral bonding. The formation of these polyhedra-slightly distorted boron cuboctahedra-appears to be dependent upon the defective nature of the tungsten-deficient metal sublattice. This previously unidentified structure type has an intermediary relationship between MB 2 and MB 12 type boride polymorphs. Manipulation of the fractionally occupied metal and boron sites may provide insight for the rational design of new superhard metals.A s demand increases for new superhard materials, the introduction of transition metal borides as candidate compounds has recently attracted a great deal of attention (1-4). This trend is at least partially driven by a need for greater efficiency in cutting tools compared with tungsten carbide (which is not superhard), as well as the shortcomings of the traditional superhard compounds-diamond (which is unusable for cutting ferrous materials) (5) and cubic boron nitride (which is very expensive to synthesize and difficult to shape) (6). Within the rapidly growing family of superhard borides, tungsten tetraboride (or WB 4 ) is of specific interest due to its excellent mechanical properties and its relatively lower cost compared with borides such as ReB 2 , OsB 2 , RuB 2 , and RhB 2 , which contain platinum group metals (3, 7-11). For instance, tungsten tetraboride demonstrates an extremely high indentation hardness of ∼43 GPa by the Vickers method (under an applied load of 0.49 N) (8) and ∼41.7 GPa by nanoindentation (maximum, at a penetration depth of 95.25 nm; Fig. 1), and can sustain a differential stress (a lower-bound estimate of compressive yield strength) of up to ∼19.7 GPa (12). More dramatically, it is like ReB 2 (2), capable of scratching natural diamond (11). We have, furthermore, previously shown that the hardness of this compound may be enhanced by the creation of solid solutions with other transition metals (9). However, to understand the underlying mechanisms for the hardness enhancements observed in WB 4 solid solutions, as well as to guide the design of new superhard borides with tailored mechanical properties, it is crucial to understand the crystal structure of this compound.Perhaps surprisingly for a simple binary ...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 96%

mentioning

confidence: 99%

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Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Lech

Turner

Mohammadi

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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113

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Borides: Solid‐State Chemistry

Fokwa

2014

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Boron forms compounds with most other elements. In addition to numerous binary and ternary compounds with metals—the true borides—boron forms related compounds with carbon, silicon, nitrogen, phosphorus, arsenic, oxygen, sulfur, and selenium. These related compounds are formed by elements more electronegative than boron and cannot therefore be denoted as borides. They display, however, similar properties and structures as borides, and are, therefore, included in this article. Borides are to some extent related to carbides and nitrides. All three groups of compounds are compounds between small nonmetal and larger metal atoms. They are occasionally denoted interstitial compounds, as the small nonmetal atoms often occupy the interstices between the metal atoms in metal‐rich compounds. In boron‐rich compounds, however, boron octahedra or icosahedra form a continuous three‐dimensional network. Most borides are characterized by high melting points, extreme hardness, brittleness, high chemical stability, and high inertness toward reactive metals. The borides are nonmolecular compounds and knowledge of the crystal structure is consequently of very high importance to characterize a boride phase. The structural principles of mainly the binary and ternary borides are described in this article. There are a total number of at least 1000 binary and ternary borides known at present. The chemical bonding in borides has evident contributions from covalent, ionic as well as metallic bonding, which explains some of the unique properties of the borides. As a rule, phases containing a large proportion of boron are semiconductors, whereas those with a lower proportion of boron are metallic conductors. TiB 2 and MgB 2 (superconductor below 39 K) are good metallic conductors, whereas MeB 6 phases are either semiconductors or metallic conductors depending on the metal. Many theoretical calculations are available, in particular of diborides, including the superconductor MgB 2 . The uses of borides and related compounds are mainly based on their hardness, chemical inertness, and magnetic and electrical properties. A few examples may be mentioned. B 4 C and cubic BN are used as abrasives, B 4 C and hexaborides as surface coatings, and CaB 6 as deoxidation agent in some metallurgical processes. TiB 2 is used in the production of vaporization boats for aluminum. It is also used in the industrial production process for aluminum owing to its high electrical conductivity and inertness toward liquid aluminum. Nd 2 Fe 14 B is, at room temperature, the strongest permanent magnetic material known. Large single crystals of YB 66 are used for monochromating synchrotron radiation.

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Superhard Materials: Advances in the Search and Synthesis of New Materials

Pangilinan

Akopov

et al. 2021

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Materials with superior hardness can be categorized as ultrahard (Vickers hardness, H v ≥ 80 GPa) and superhard ( H v ≥ 40 GPa). These materials are commonly used as cutting tools and abrasives in the machining and manufacturing industries. With its extreme hardness, diamond is the best known and most used ultrahard material for industrial applications. However, it is ineffective at cutting and drilling ferrous alloys due to diamond's high reactivity with iron and poor thermal stability in air. Additionally, the synthesis of diamond requires both high pressure (HP) and high temperature, making it an expensive process. These limitations have driven the search for alternative superhard materials that are capable of cutting steels and other materials at lower costs. This article reviews the concept of hardness and summarizes advancements in the synthesis and mechanical properties of hard materials. It begins with a review of methods to measure hardness, adding HP diffraction methods to more conventional hardness measurements. It then considers new ultrahard materials that exist within the B–C–N ternary system, with hardness approaching diamond but improved chemical stability. Finally, it surveys superhard nitrides, oxides, and borides as potential alternative materials, focusing on transition metal boride systems where the synthesis can be readily achieved at ambient pressure and scaled for industrial applications. We hope that this article serves as an overview of hard materials and guide for the comparison of data reported in the literature.

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Toward Inexpensive Superhard Materials: Tungsten Tetraboride-Based Solid Solutions

Cited by 109 publications

References 31 publications

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Borides: Solid‐State Chemistry

Superhard Materials: Advances in the Search and Synthesis of New Materials

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Toward Inexpensive Superhard Materials: Tungsten Tetraboride-Based Solid Solutions

Cited by 109 publications

References 31 publications

Structure of superhard tungsten tetraboride: A missing link between MB 2 and MB 12 higher borides

Structure of superhard tungsten tetraboride: A missing link between MB 2 and MB 12 higher borides

Borides: Solid‐State Chemistry

Superhard Materials: Advances in the Search and Synthesis of New Materials

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Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides

Structure of superhard tungsten tetraboride: A missing link between MB ₂ and MB ₁₂ higher borides