The influence of carbon on the microstructure and mechanical properties of sintered boron carbide

Schwetz, Karl A.; Grellner, Wolfgang

doi:10.1016/0022-5088(81)90195-8

Cited by 148 publications

(53 citation statements)

References 6 publications

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“…We also computed the Knoop hardness using the electronegativity approach [38,39], leading to a value of 31.7 GPa. These results are in good agreement with previous calculations and experimental data [2,3,[40][41][42]. The equations of states for various B 4 C stoichiometric structures are shown in Fig.…”

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confidence: 82%

Atomistic Explanation of Shear-Induced Amorphous Band Formation in Boron Carbide

2014

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Boron carbide (B 4 C) is very hard, but its applications are hindered by stress-induced amorphous band formation. To explain this behavior, we used density function theory (Perdew-Burke-Ernzerhof flavor) to examine the response to shear along 11 plausible slip systems. We found that the ð0111Þ=h1101i slip system has the lowest shear strength (consistent with previous experimental studies) and that this slip leads to a unique plastic deformation before failure in which a boron-carbon bond between neighboring icosahedral clusters breaks to form a carbon lone pair (Lewis base) on the C within the icosahedron. Further shear then leads this Lewis base C to form a new bond with the Lewis acidic B in the middle of a CBC chain. This then initiates destruction of this icosahedron. The result is the amorphous structure observed experimentally. We suggest how this insight could be used to strengthen B 4 C. DOI: 10.1103/PhysRevLett.113.095501 PACS numbers: 61.50.Ks, 62.20.M-, 64.70.-p, 82.40.Fp Boron carbide (B 4 C) exhibits such novel properties as high melting temperature, high thermal stability, high hardness, low density, and high abrasion resistance [1][2][3][4][5][6][7][8][9][10][11]. The combination of these properties makes it widely useful in refractory applications, as abrasive powders, in body armor, and as a neutron radiation absorbent [1][2][3][4]. However, the brittle failure under impact exhibited by B 4 C prevents the wide insertion of boron carbide into extended engineering applications. Although B 4 C has a high Hugoniot elastic limit (HEL) of 17-20 GPa, approximately twice that of normal ceramics, it fractures easily just above the HEL at high impact velocities and pressures [12][13][14][15]. Chen et al. reported the observation of shock-induced local amorphization bands that might be responsible for the low fracture toughness of B 4 C [6]. In addition, amorphization bands had been observed in nanoindentation and scratch experiments, where the loading rate is much lower than for dynamical shock loading [16][17][18][19]. Particularly, recent nanoindentation experiments revealed amorphous shear bands along the (0111) plane [19]. Indeed, the same amorphous shear band has been observed experimentally in boron suboxide (B 6 O) [20]. An attempt to understand this through Gibbs free-energy calculations based on density functional theory suggested that the ðB 12 ÞCCC structure provides a possible source of failure of boron carbide just above the HEL [7]. However, despite these extensive experimental and theoretical efforts, the atomistic mechanism underlying pressure-induced amorphization and phase transitions of boron carbide is still not known [3].Stressed materials normally dissipate the accumulating elastic energy through plastic deformation that is mediated by dislocation slip and deformation twinning in metallic systems. Unlike these general deformation mechanisms in conventional metallic materials, we find that boron carbide deforms by atomic scale amorphous band formation, a particular mode of deforma...

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confidence: 82%

Atomistic Explanation of Shear-Induced Amorphous Band Formation in Boron Carbide

2014

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“…A value of 1.9MPam la was determined by Hollenberg$ [ 13] using the double torsion technique. Mecholsky et al [15] determined a value of about 3.7MPa m 1/2 using the double cantilever beam technique and Schwetz et al [19] recently reported a value of 3.6MPam 1/2 using the single edge notched beam test. Our value (3.67MPam l/z) compares favourably with the two latter values.…”

Section: Materials Characteristicsmentioning

confidence: 98%

High temperature fracture of boron carbide: experiments and simple theoretical models

With

1984

J Mater Sci

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The mechanical properties of theoretically dense boron carbide with a grain size of about 10/am have been investigated as a function of temperature. It was found that the fracture toughness remained constant at ~ 3.7 MPa m 1/2 up to 1500 K and there was little or no decrease in strength from its room temperature value of "~ 350 MPa. Both the order of magnitude and the temperature dependence of the fracture energy, calculated from the fracture toughness and elastic data, can be explained in terms of simple theoretical models.

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“…Second, during the later sintering period, the carbon particles migrate with the boundary, thereby controlling grain growth, until they are agglomerated as graphite aggregates at boron carbide grain corners (2).…”

Section: Microstructurementioning

confidence: 99%

“…Geometric simple shapes and pellets can be easily fabricated by a press-and-sinter process, developed in the late 1970s, which uses boron carbide powders of submicrometer particle size (specific surface area, 10-20 m/g) and firing of dry pressed compacts in inert atmospheres to temperatures near 2150°C (2).…”

Section: Introductionmentioning

confidence: 99%

Mechanical Properties of Injection Molded B4C–C Ceramics

Schwetz¹,

Sigl²,

Pfau³

1997

Journal of Solid State Chemistry

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The influence of carbon on the microstructure and mechanical properties of sintered boron carbide

Cited by 148 publications

References 6 publications

Atomistic Explanation of Shear-Induced Amorphous Band Formation in Boron Carbide

Atomistic Explanation of Shear-Induced Amorphous Band Formation in Boron Carbide

High temperature fracture of boron carbide: experiments and simple theoretical models

Mechanical Properties of Injection Molded B4C–C Ceramics

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