Boron suboxide materials with Co sintering additives

Johnson, Oluwagbenga T.; Sigalas, Iakovos; Ogunmuyiwa, Enoch Nifise; Kleebe, Hans‐Joachim; Müller, Mathis M.; Herrmann, Matthias

doi:10.1016/j.ceramint.2010.02.035

Cited by 24 publications

(21 citation statements)

References 17 publications

(26 reference statements)

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“…In general, the micrograph shows a homogeneous B 6 O microstructure with visible pores on the specimen surface as a direct result of some considerable practical challenges in the densification of B 6 O by hot pressing [1,10,11]. The analysis of the surface composition by EDX is also indicative of nominally pure B 6 O phase.…”

Section: Surface Characterizationmentioning

confidence: 97%

“…5 Using a simple code written in MATLAB we have selected and collected ten equally spaced data points, (P (i) , h (i) ), from the experimentally measured loading P − h data. Given the observation and assumptions alluded to in the previous paragraph, we can speculate that if a sequence of ten loading-unloading nanoindentation cycles were to be carried out at the same position at load in the range P (1) to P (10) , then the MATLAB subroutine-collected (P (i) , h (i) ) could easily be the new set of data defining the maximum load and maximum indentation size defined as (P …”

Section: Tablementioning

confidence: 99%

“…Reasons for this include the low fracture toughness of hot-pressed B 6 O materials [11], considerable practical challenges in the densification of the material [1,3,10,11], stoichiometric B 6 O samples are not easy to synthesize [1,3,10], and the poor crystallinity [1,11]. As a result, numerous mechanical properties of the material are still poorly understood [12].…”

Section: Introductionmentioning

confidence: 96%

“…Although the hot-pressed B 6 O materials exhibit a rather unusual and wide range of superior properties such as high hardness with low density, high mechanical strength, and high chemical inertness [1,3,10], the commercial applications are yet to be realized. Reasons for this include the low fracture toughness of hot-pressed B 6 O materials [11], considerable practical challenges in the densification of the material [1,3,10,11], stoichiometric B 6 O samples are not easy to synthesize [1,3,10], and the poor crystallinity [1,11].…”

Section: Introductionmentioning

confidence: 99%

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Nanoindentation hardness of hot-pressed boron suboxide

Machaka¹,

Derry²,

Sigalas³

2011

Materials Science and Engineering: A

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Section: Surface Characterizationmentioning

confidence: 97%

Section: Tablementioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Nanoindentation hardness of hot-pressed boron suboxide

Machaka¹,

Derry²,

Sigalas³

2011

Materials Science and Engineering: A

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“…Attempts to enhance the mechanical properties of boron suboxide with high-pressure techniques have been made by fabricating boron suboxide-based composites with other materials, e.g. diamond [73], cBN [74], boron carbide [68,75,76], titanium diboride [77], and some metal oxide additives [78][79][80]. A significant improvement in the mechanical properties of boron suboxide-based composites have recently been highlighted by the work of Solodkyi et al [68], in which they fabricated boron suboxide-boron carbide composites, using the spark plasma sintering (SPS) method.…”

Section: Boron Suboxidementioning

confidence: 99%

First-principles study of configurational disorder in icosahedral boron-rich solids

Ektarawong¹

2015

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This thesis is a theoretical study of configurationally disordered icosahedral boronrich solids, in particular boron carbides, using density functional theory and alloy theory. The goal is to resolve discrepancies, regarding the properties of boron carbides, between experiments and previous theoretical calculations which have been a controversial issue in the field of icosahedral boron-rich solids. For instance, B 13 C 2 is observed experimentally to be a semiconductor, meanwhile electronic band structure calculations reveal a metallic character of B 13 C 2 due to its electron deficiency. In B 4 C, on the other hand, the experimentally observed band gap is unexpectedly smaller, not the usual larger, than that of standard DFT calculations. Another example is given by the existence of a small structural distortion in B 4 C, as predicted in theoretical calculations, which reduces the crystal symmetry from the experimentally observed rhombohedral (R3m) to the based-centered monoclinic (Cm). Since boron carbide is stable as a single-phase over a broad composition range (∼8-20 at.% C), substitution of boron and carbon atoms for one another is conceivable. For this reason, the discrepancies have been speculated in the literature, without a proof, to originate from configurational disorder induced by substitutional defects. However, owing to its complex atomic structure, represented by 12-atom icosahedra and 3-atom intericosahedral chains, a practical alloy theory method for direct calculations of the properties of the relevant configurations of disordered boron carbides, as well as for a thermodynamic assessment of their stability has been missing.In this thesis, a new approach, the superatom-special quasirandom structure (SA-SQS), has been developed. The approach allows one to model configurational disorder in boron carbide, induced by high concentrations of low-energy B/C substitutional defects. B 13 C 2 and B 4 C are the two stoichiometries, mainly considered in this study, as they are of particular importance and have been in focus in the literature. The results demonstrate that, from thermodynamic considerations, both B 13 C 2 and B 4 C configurationally disorder at high temperature. In the case of B 13 C 2 , the configurational disorder splits off some valence states into the band gap that in turn compensates the electron deficiency in ordered B 13 C 2 , thus resulting in a semiconducting character. As for B 4 C, the configurational disorder eliminates the monoclinic distortion, thus resulting in the restoration of the higher rhombohedral symmetry. Configurational disorder can also account for an exceliii iv lent agreement on elastic moduli of boron carbide between theory and experiment. Thus, several of the previous discrepancies between theory and experiments are resolved.Inspired by attempts to enhance the mechanical properties of boron suboxide by fabricating boron suboxide-boron carbide composites, as recently suggested in the literature, the SA-SQS approach is used for modeling mixtures of boron sub...

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Superhard Materials

Mohammadi

Kaner

2012

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Materials possessing superior hardness can be divided into two main categories: ultra‐hard and superhard. Diamond and cubic boron nitride ( c ‐BN) are considered ultra‐hard with hardness values ranging from 70 to 110 and 45 to 60 GPa, respectively. All other materials with a hardness of greater than 40 GPa are called superhard. Ultra‐hard materials are traditionally used in industrial applications including cutting tools and wear‐protecting surfaces. However, diamond is not a good choice for high‐speed cutting of ferrous‐based alloys because of its graphitization on the material's surface and formation of brittle carbides, which leads to poor cutting performance. In addition, the synthesis of both diamond and c ‐BN requires high pressure‐high temperature conditions. Therefore, a great deal of effort has been made to address these shortcomings and to find a reliable substitute for these ultra‐hard materials. Studies have been directed toward the development of either main group compounds (such as SiC and Si 3 N 4 ) or transition‐metal compounds (such as WC and HfN). Unfortunately, most of these compounds are not superhard (e.g., WC, SiC) or their synthesis needs high pressures and high temperatures (e.g., Si 3 N 4 ) that entails expensive equipment and processing costs. Among these compounds, dense transition‐metal diborides have exhibited very promising mechanical properties including great hardness, while remaining relatively easy to synthesize at ambient pressure, and may form the next generation of cutting tools and abrasion‐resistant coatings. In this article, we will review the recent advancements in synthesis and characterization of single‐phase ultra‐hard and superhard materials, with a special focus on transition‐metal diborides. We hope that this article may shed light on the inconsistencies of some of the data reported in the literature and make comparisons among materials possessing great hardness easier. Except for some rare cases, the hardness of thin films and composites will not be covered here and left for a future study.

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Boron suboxide materials with Co sintering additives

Cited by 24 publications

References 17 publications

Nanoindentation hardness of hot-pressed boron suboxide

Nanoindentation hardness of hot-pressed boron suboxide

First-principles study of configurational disorder in icosahedral boron-rich solids

Superhard Materials

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