Composition and crystallographic data for the highest boride of tungsten

Romans, P. A.; Krug, Marion P.

doi:10.1107/s0365110x6600063x

Cited by 76 publications

(70 citation statements)

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“…1 displays the X-ray diffraction (XRD) pattern of a tungsten tetraboride (WB 4 ) sample synthesized by arc melting. The XRD pattern matches very well with the reference data available for this material in the Joint Committee on Powder Diffraction Standards (JCPDS) database (24). The WB 4 pattern clearly shows that no crystalline impurity phases, such as tungsten diboride (WB 2 with major peaks at 2θ ¼ 25.683°, 34.680°and 35.275°), are present.…”

supporting

confidence: 65%

“…Because the purity of superhard materials directly influences their mechanical properties (29), the existence of other borides of tungsten in the samples might explain the anomalously low bulk modulus. Making solid ingots of phase pure WB 4 is especially challenging because the tungstenboron phase diagram indicates that WB 2 is thermodynamically favorable with any W∶B molar ratio below 1∶12 (24).…”

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confidence: 99%

“…Tungsten is one of the few transition metals that is known for its ability to form higher boron content borides. In addition to tungsten diboride (WB 2 ), which is not superhard (22,23), tungsten is able to form tungsten tetraboride (WB 4 ), the highest boride of tungsten that exists under equilibrium conditions (24)(25)(26). The advantage of this material over other borides are: (i) Both tungsten and boron are relatively inexpensive, (ii) the lower metal content in the higher borides reduces the overall cost of production because the more costly transition metal is being replaced by less expensive boron thus reducing the cost per unit volume, and (iii) the higher boron content lowers the overall density of the structure, which could be beneficial in applications where lighter weight is an asset.…”

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Tungsten tetraboride, an inexpensive superhard material

Mohammadi

Lech

Xie

et al. 2011

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

312

281

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Tungsten tetraboride (WB 4 ) is an interesting candidate as a less expensive member of the growing group of superhard transition metal borides. WB 4 was successfully synthesized by arc melting from the elements. Characterization using powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthesized material is phase pure. The zeropressure bulk modulus, as measured by high-pressure X-ray diffraction for WB 4 , is 339 GPa. Mechanical testing using microindentation gives a Vickers hardness of 43.3 AE 2.9 GPa under an applied load of 0.49 N. Various ratios of rhenium were added to WB 4 in an attempt to increase hardness. With the addition of 1 at.% Re, the Vickers hardness increased to approximately 50 GPa at 0.49 N. Powders of tungsten tetraboride with and without 1 at.% Re addition are thermally stable up to approximately 400°C in air as measured by thermal gravimetric analysis.dispersion hardening | indentation hardness | intrinsic hardness | nano-indentation hardness | solid solutions I n many manufacturing processes, materials must be cut, formed, or drilled, and their surfaces protected with wearresistant coatings. Diamond has traditionally been the material of choice for these shaping operations, due to its superior mechanical properties (e.g., hardness > 70 GPa) (1, 2). However, diamond is rare in nature and difficult to synthesize artificially due to the need for a combination of high temperature and high pressure. Industrial applications of diamond are thus generally limited by cost. Moreover, diamond is not a good option for high-speed cutting of ferrous alloys due to its graphitization on the material's surface and formation of brittle carbides, which leads to poor cutting performance (3). Other hard or superhard (hardness ≥ 40 GPa) substitutes for diamond include compounds of light elements such as cubic boron nitride (4) and BC 2 N (5) or transition metals combined with light elements such as WC (6), HfN (7), and TiN (8). Although the compounds of the first group (B, C, or N) possess high hardness, their synthesis requires high pressure and high temperature and is thus nontrivial (9, 10). On the other hand, most of the compounds of the second group (transition metal-light elements) are not superhard although their synthesis is more straightforward.To overcome the shortcomings of diamond and its substitutes, we have been pursuing the synthesis of dense transition metal borides, which combine high hardness with synthetic conditions that do not require high pressure (11,12). For example, arc melting and metathesis reactions have been used to synthesize the transition metal diborides OsB 2 (13, 14), RuB 2 (15), and ReB 2 (16-20). Among these, rhenium diboride (ReB 2 ) with a hardness of approximately 48 GPa under a load of 0.49 N has proven to be the hardest (16, 21). The boron atoms are needed to build the strong covalent metal-boron and boron-boron bonds that are responsible for the high hardness of these materials (12). Because of this, it is expected th...

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confidence: 65%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Tungsten tetraboride, an inexpensive superhard material

Mohammadi

Lech

Xie

et al. 2011

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

312

281

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“…The crystal structure of ReB 2 ( Fig. 8(a) The most widely cited structure of WB 4 was originally assigned by Romans and Krug in 1966, 13 which consists of alternating layers of hexagonal network of boron and hexagonal layers of tungsten atoms (Fig. 8(b)).…”

Section: Discussionmentioning

confidence: 99%

“…It is the highest boride formed under normal pressures. [13][14][15] Interestingly, the structure of WB 4 exhibits a unique covalent bonding network with B-B covalent bonds aligned along the caxis. 16 This covalent bonding framework of WB 4 should result in a more isotropic structure than that exhibited by ReB 2 .…”

Section: Introductionmentioning

confidence: 99%

Exploring the high-pressure behavior of superhard tungsten tetraboride

et al. 2012

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Abstract:In this work, we examine the high pressure behavior of superhard material candidate WB 4 using high-pressure synchrotron X-ray diffraction in a diamond anvil cell up to 58.4 GPa. The zero-pressure bulk modulus, K 0 , obtained from fitting the pressure-volume data using the second-order Birch-Murnaghan equation of state is 326 ± 3 GPa. A reversible, discontinuous change in slope in the c/a ratio is further observed at ~42 GPa, suggesting that lattice softening occurs in the c direction above this pressure. This softening is not observed in other superhard transition metal borides such as ReB 2 compressed to similar pressures. Speculation on the possible relationship between this softening and the orientation of boronboron bonds in the c direction in the WB 4 structure is included. Finally, the shear and Young's modulus values are calculated using an isotropic model based on the measured bulk modulus and an estimated Poisson's ratio for WB 4 .

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