Field-assisted Densification of Superhard B6O Materials with Y2O3/Al2O3 Addition

Herrmann, Mathias; Raethel, Jan; Sempf, Kerstin; Thiele, Maik; Bales, Axel; Sigalas, Iakovos

doi:10.1007/978-90-481-9818-4_21

Cited by 4 publications

(10 citation statements)

References 13 publications

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“…These light elements have the ability to form covalently bonded 3D networks with a high atomic density and extreme resistance to external shear. B 6 O is a particularly promising material system for light‐weight armor applications as it has a high hardness, low density, high mechanical strength, high oxidation resistance (<1200°C), and chemical inertness . However, unlike other high‐performance ceramics, B 4 C and B 6 O display low fracture toughness and a reduction in shear strength under extreme high temperature and pressure environmental conditions.…”

Section: Introductionmentioning

confidence: 99%

Carbon Doping in Boron Suboxide: Structure, Energetics, and Elastic Properties

2015

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The structural, electronic, and elastic properties of pristine and carbon‐doped boron suboxide (B6O) are calculated using density functional theory. The results indicate that it is energetically preferable for a single carbon atom to substitute into an oxygen site rather than a boron site. The lattice parameters and cell volume increase to relieve the residual stress created by the carbon substitution. The interstitial position is not favorable for a single atom substitution. However, if two carbon atoms substitute for two neighboring oxygen atoms, then it becomes energetically favorable to dope an interstitial oxygen, boron, or carbon atom along the C–C chain. If the interstitial dopant is either boron or carbon, a local B4C‐like structure with either a C–B–C or C–C–C chain is created within the boron suboxide unit cell. The resulting structure shows improvements in the bulk modulus at the expense of the shear and Young's moduli. The moduli further improve if an additional carbon is substituted within a polar or equatorial site of the neighboring B12 icosahedron. Based on these calculations, we conclude that carbon doping can either harden or soften B6O depending on the manner in which the substitutions are populated. Furthermore, as B6O samples are often oxygen deficient, C doping can occupy such sites and improve the elastic properties.

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Section: Introductionmentioning

confidence: 99%

Carbon Doping in Boron Suboxide: Structure, Energetics, and Elastic Properties

2015

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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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“…Boron and boron‐rich compounds are characterized by unique bonding properties and crystal structures, which give rise to a variety of mechanical properties, making them as indispensable materials for high‐temperature applications . Owing to strong covalent bonding, these ceramics show high stability at elevated temperatures and good high‐temperature strength.…”

Section: Introductionmentioning

confidence: 99%

“…Among the covalent oxides, boron‐suboxide‐based ceramic composites have been extensively studied as alternatives to boron carbide . Single‐phase boron suboxide (B 6 O) possesses high hardness (>28 GPa), good high‐temperature hardness, and chemical stability.…”

Section: Introductionmentioning

confidence: 99%

“…This “superhardness” with a value of ~55 GPa corresponds to a load of 0.25 N. However, even hard boron suboxide exhibits low fracture toughness, which limits its potential application. Hence, one of the most popular methods of overcoming this obstacle is to fabricate B 6 O‐based composites, which have been most widely reported in studies of Herrmann et al However, an increase in fracture toughness to 5 MPa/m 2 is usually accompanied by a significant decrease in hardness (25 GPa at a load of 3.92 N) . In addition, boron‐suboxide‐based ceramics possess a high hardness to flexural strength ratio (Fig.…”

Section: Introductionmentioning

confidence: 99%

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High‐Temperature Strength of Boron Suboxide Ceramic Consolidated by Spark Plasma Sintering

et al. 2016

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The spark plasma sintering (SPS) of B6O ceramics using a highly crystalline boron suboxide powder with a low oxygen deficiency level is reported. The monolithic boron suboxide ceramic exhibited a room‐temperature strength of 300 ± 20 MPa, which is comparable to the strength of monolithic boron carbide. With increasing flexural test temperature, the strength of the boron suboxide ceramics increased to 450 MPa at 1400°C. The increase in strength with the temperature is associated with the unique microstructure of boron suboxide grains, which allows intergranular “brittle” fracture along subgrains even at 1400°C. This suggests that even higher strengths can be achieved.

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Field-assisted Densification of Superhard B6O Materials with Y2O3/Al2O3 Addition

Cited by 4 publications

References 13 publications

Carbon Doping in Boron Suboxide: Structure, Energetics, and Elastic Properties

Carbon Doping in Boron Suboxide: Structure, Energetics, and Elastic Properties

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

High‐Temperature Strength of Boron Suboxide Ceramic Consolidated by Spark Plasma Sintering

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