Formation process of tungsten borides by solid state reaction between tungsten and amorphous boron

Itoh, Hideaki; Matsudaira, Tsuneaki; Naka, Shigeharu; Hamamoto, Hiroshi; Obayashi, Mikio

doi:10.1007/bf01086475

Cited by 87 publications

(67 citation statements)

References 6 publications

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“…The excess boron is needed to ensure the thermodynamic stability of the WB 4 structure based on the binary phase diagram of the tungsten-boron system (24,26). Furthermore, to test the possibility of increasing the hardness, rhenium (99.99%, CERAC Inc.) was substituted for tungsten at different concentrations of 0.5-50.0 at.%.…”

Section: Methodsmentioning

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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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.

317

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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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Tungsten tetraboride, an inexpensive superhard material

Mohammadi

Lech

Xie

et al. 2011

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

317

281

View full text Add to dashboard Cite

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“…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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“…With fieldactivated combustion synthesis [22][23][24], WB 2 was shown to form solid solutions with TiB 2 and CrB 2 from elemental reactants. Itoh et al [25] prepared various tungsten borides by solid state reactions between tungsten and boron powers at 800-1550 8C, and indicated that optimum production of WB and W 2 B 5 was attained in the samples with a nearly 10 at.% excess of boron. Peshev et al [26,27] performed a series of experiments on the borothermic reduction of different metal www.elsevier.com/locate/ceramint oxides between 1000 and 1750 8C to prepare the corresponding metal borides, including CrB 2 , Mo 2 B 5 , W 2 B 5 , VB 2 , NbB 2 , and TaB 2 .…”

Section: Introductionmentioning

confidence: 98%