Phase diagram of the system tungsten-Boron

Portnoi, K. I.; Romashov, V. M.; Levinskii, Yu. V.; Romanovich, I. V.

doi:10.1007/bf00775398

Cited by 22 publications

(14 citation statements)

References 6 publications

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“…The decrease in strength of both as-sintered and annealed ceramics as temperature increased from 1500°C to 1800°C may be related to simultaneous changes in the WB and W deformation mechanism, which has been shown to occur at about half of the melting temperature (T melt = 2740°C for WB, so 0.6T melt is 1644°C). [36,37] For both ceramics, the microstructure of the fractured bars did not change when tested at 1800°C in argon. In contrast, testing in air at 1500°C resulted in formation of an oxidized scale that was around 20 µm thick.…”

Section: Mechanical Propertiesmentioning

confidence: 94%

A simple route to fabricate strong boride hierarchical composites for use at ultra-high temperature

Silvestroni

Gilli

Migliori

et al. 2020

Composites Part B: Engineering

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A simple method to obtain a highly refractory HfB 2 -based ceramic nano-composite is presented. The boride was hot pressed with additions of SiC and WC particles and subsequently annealed at 2100°C for 2 hours.The annealing procedure was beneficial for high temperature strength, which increased by about 300 MPa in the 1500°C to 1800°C temperature range compared to the as-sintered material. Peak strengths of 850 MPa at 1500°C and 650 MPa at 1800°C were achieved due to two main microstructural changes. First, rounded SiC particles that were surrounded by a silica-based glass in the as-sintered ceramics evolved into platelets with mostly clean grain boundaries after heat treatment. In addition, the (Hf,W)B 2 solid solution that formed as shells around HfB 2 grain cores during densification reached an equilibrium state after annealing that revealed nano-texturing of the shell, which constituted a nano-composite with metallic W nano-particles embedded within HfB 2 grains. These two features combined to contribute to refractoriness and increased strength at elevated temperature. The unique findings reported in this study launch significant opportunities for ceramic development, manufacturing, and applications.

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Section: Mechanical Propertiesmentioning

confidence: 94%

A simple route to fabricate strong boride hierarchical composites for use at ultra-high temperature

Silvestroni

Gilli

Migliori

et al. 2020

Composites Part B: Engineering

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“…In the vicinity of the arc, temperatures above the melting point of W are reached, which is higher than the melting points of the compounds [68][69][70]. So, melting and segregation effects are expected.…”

Section: 72mentioning

confidence: 99%

Collection strategy, inner morphology, and size distribution of dust particles in ASDEX Upgrade

et al. 2014

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Abstract.The dust collection and analysis strategy in ASDEX Upgrade (AUG) is described. During five consecutive operation campaigns (2007)(2008)(2009)(2010)(2011), Si collectors were installed, which were supported by filtered vacuum sampling and collection with adhesive tapes in 2009. The outer and inner morphology (e.g. shape) and elemental composition of the collected particles were analysed by scanning electron microscopy. The majority of the ~50000 analysed particles on the Si collectors of campaign 2009 contain tungsten -the plasma-facing material in AUG -and show basically two different types of outer appearance: spheroids and irregularly shaped particles. By far most of the W-dominated spheroids consist of a solid W core, i.e., solidified W droplets. A part of these particles is coated with low Z material; a process which seems to happen presumably in the far scrape off layer plasma. In addition, some conglomerates of B, C, and W appear as spherical particles after their contact with plasma. By far most of the particles classified as B-, C-, and W-dominated irregularly shaped particles consist of the same conglomerate with varying fraction of embedded W in the B-C matrix and some porosity, which can exceed 50%. The fragile structures of many conglomerates confirm the absence of intensive plasma contact. Both the ablation and mobilization of conglomerate material and the production of W droplets are proposed to be triggered by arcing. The size distribution of each dust particle class is best described by a lognormal distribution allowing an extrapolation of the dust volume and surface area. The maximum in this distribution is observed above the resolution limit of 0.28 µm only for the W-dominated spheroids, at around 1 µm. The amount of W-containing dust is extrapolated to be less than 300 mg on the horizontal areas of AUG.

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“…Fortunately, tungsten tetraboride (Figure ) is a very adaptable structure, containing metal vacancies and voids, , and it can accommodate metal atoms as interstitial dopants in addition to traditional substitutional doping. Substitutional doping in the form of alloying and solid-solution formation can greatly enhance hardness through not only intrinsic but also extrinsic effects. ,,− Tungsten tetraboride is an incongruently melting phase, requiring excess boron in order to form by direct heating . It is typically prepared using a W:B ratio of 1:12, and at this composition, the only products are tungsten tetraboride and β-rhombohedral boron; otherwise at lower metal to boron ratios, a lower tungsten diboride forms. , …”

Section: Introductionmentioning

confidence: 99%

Effects of Variable Boron Concentration on the Properties of Superhard Tungsten Tetraboride

et al. 2017

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Tungsten tetraboride is an inexpensive, superhard material easily prepared at ambient pressure. Unfortunately, there are relatively few compounds in existence that crystallize in the same structure as tungsten tetraboride. Furthermore, the lack of data in the tetraboride phase space limits the discovery of any new superhard compounds that also possess high incompressibility and a three-dimensional boron network that withstands shear. Thus, the focus of the work here is to chemically probe the range of thermodynamically stable tetraboride compounds with respect to both the transition metal and the boron content. Tungsten tetraboride alloys with a variable concentration of boron were prepared by arc-melting and investigated for their mechanical properties and thermal stability. The purity and phase composition were confirmed by energy dispersive X-ray spectroscopy and powder X-ray diffraction. For variable boron WB, it was found that samples prepared with a metal to boron ratio of 1:11.6 to 1:9 have similar hardness values (∼40 GPa at 0.49 N loading) as well as having a similar thermal oxidation temperature of ∼455 °C. A nearly single phase compound was successfully stabilized with tantalum and prepared with a nearly stoichiometric amount of boron (4.5) as WTaB. Therefore, the cost of production of WB can be decreased while maintaining its remarkable properties. Insights from this work will help design future compounds stable in the adaptable tungsten tetraboride structure.

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Phase diagram of the system tungsten-Boron

Cited by 22 publications

References 6 publications

A simple route to fabricate strong boride hierarchical composites for use at ultra-high temperature

A simple route to fabricate strong boride hierarchical composites for use at ultra-high temperature

Collection strategy, inner morphology, and size distribution of dust particles in ASDEX Upgrade

Effects of Variable Boron Concentration on the Properties of Superhard Tungsten Tetraboride

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