Electronic structures and mechanical properties of boron and boron-rich crystals (Part 2)

Shirai, Katsuhiko

doi:10.3103/s1063457610050059

Cited by 21 publications

(17 citation statements)

References 71 publications

(81 reference statements)

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“…[1][2][3][4][5][6][7][8][9][10] However, engineering applications of B 4 C to body armor or abrasive powders have been impeded by the abnormal brittle failure under high pressure due to amorphous shear band formation. 5,10,11 Amorphous bands had also been observed in both simulated shear and scratch experiments, [11][12][13][14] suggesting that it is a major failure mechanism in B 4 C, but it is not known what role is played by grain boundaries (GBs).…”

Section: Introductionmentioning

confidence: 99%

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Yang

Coleman

LaSalvia

et al. 2018

ACS Appl. Mater. Interfaces

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Abstract:The role that grain boundaries (GB) can play on mechanical properties has been studied extensively for metals and alloys. However, for covalent solids such as boron carbide (B 4 C), the role of GB on the inelastic response to applied stresses is not well established. We consider here the unusual ceramic, boron carbide (B 4 C), which is very hard and lightweight but exhibits brittle impact behavior. We used quantum mechanics (QM) simulations to examine the mechanical response in atomistic structures that model GBs in B 4 C under pure shear and also with biaxial shear deformation that mimics indentation stress conditions. We carried out these studies for two simple GB models including also the effect of adding Fe atoms (possible sintering aid and/or impurity) to the GB. We found that the critical shear stresses of these GB models are much lower than for crystalline and twinned B 4 C. The two GB models lead to different interfacial energies. The higher interfacial energy at the GB only slightly decreases the critical shear stress but dramatically increases the critical failure strain. Doping the GB with Fe decreases the critical shear stress of at the boundary by 14% under pure shear deformation. In all GBs studied here, failure arises from deconstructing the icosahedra within the GB region under shear deformation. We find that Fe dopant interacts with icosahedra at the GB to facilitate this deconstruction of icosahedra. These results provide significant insight for designing polycrystalline B 4 C with improved strength and ductility.

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Section: Introductionmentioning

confidence: 99%

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Yang

Coleman

LaSalvia

et al. 2018

ACS Appl. Mater. Interfaces

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“…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].…”

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confidence: 99%

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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“…For the shear deformation, we used the supercell containing 61 atoms for (100)[001], (100)[010], and (010)[001] slip systems, and a supercell with 122 atoms for (001)[100] and (001)[110] slip systems in which the unit cell is replicated twice along [100 ] and [110] directions, respectively. The supercell with 122 atoms was employed for (001) slip plane since the (001) plane corresponds to the (0111) slip plane in B 4 C, 9 and it is comparable to our previous simulations on B 4 C with 120 atoms in the supercell. We applied the (4 × 6 × 4) K-point grid mesh in the Brillouin zone for (100) Figure 1A.…”

Section: Methodsmentioning

confidence: 70%

“…This makes the whole system satisfy the Wade's rule. Thus, the Mg 3 B 50 C 8 can be represented by (Mg 4/3+ ) 2 (Mg 2/3+ )(B12 4/3− )4 (CB + C) 2 (C 2 ) 2 based on the above bonding analysis. From our bonding analysis, three Mg atoms filled in four partial occupation sites makes the atomic structure exactly satisfy the Wade's rule.…”

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confidence: 99%

First principles predicting enhanced ductility of boride carbide through magnesium microalloying

Tang

Goddard

et al. 2019

J Am Ceram Soc

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The low fracture toughness of strong covalent solids prevents them from wide engineering applications. Microalloying metal elements into covalent solids may lead to a significant improvement on mechanical properties and drastical changes on the chemical bonding. To illustrate these effects we employed density functional theory (DFT) to examine the bonding characteristic and mechanical failure of recently synthesized magnesium boride carbide (Mg3B50C8) that is formed by adding Mg into boron carbide (B4C). We found that Mg3B50C8 has more metallic bonding charterer than B4C, but the atomic structure still satisfies Wade's rules. The metallic bonding significantly affects the failure mechanisms of Mg3B50C8 compared with B4C. In Mg3B50C8, the B12 icosahedral clusters are rotated in order to accommodate to the extensive shear strain without deconstruction. In addition, the critical failure strength of Mg3B50C8 is slightly higher than that of B4C under indentation stress conditions. Our results suggested that the ductility of Mg3B50C8 is drastically enhanced compared with B4C while the hardness is slightly higher than B4C.

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Electronic structures and mechanical properties of boron and boron-rich crystals (Part 2)

Cited by 21 publications

References 71 publications

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

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

First principles predicting enhanced ductility of boride carbide through magnesium microalloying

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