Large indentation strain-stiffening in nanotwinned cubic boron nitride

Li, Bing; Sun, Hong; Chen, Changfeng

doi:10.1038/ncomms5965

Cited by 111 publications

(104 citation statements)

References 34 publications

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“…37 A 1% level of strain was predefined as the small strain increment for each To simulate the mechanical response under indentation experiments, we applied biaxial shear deformation on the GBs structures, adjusted to mimic the deformation under the indenter by imposing the relations σ zz = σ zx × tan Φ where σ zz is the normal stress, σ zx is the shear stress and Φ is the centerline-to face angle of the indenter (Φ = 68° for Vickers indenter). 38 The other four strain components were relaxed in the biaxial shear deformation. The residual stresses after relaxing were less than 0.2 GPa for both pure shear and biaxial shear deformation.…”

Section: Computational Methodologymentioning

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: Computational Methodologymentioning

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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“…28 To mimic the complex stress conditions under indentation experiments, we applied biaxial shear deformation where the ratio of the compressive pressure beneath the indenter normal to the chosen shear plane has a fixed fraction of the tangential shear while the other four strain components are relaxed. 29 The residual stresses after relaxing were less than 0.5 GPa for both pure shear and biaxial shear deformation. …”

Section: −25mentioning

confidence: 99%

Improved Ductility of B₁₂ Icosahedra-based Superhard Materials through Icosahedral Slip

Goddard

2017

J. Phys. Chem. C

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Boron carbide (B 4 C) is superhard but suffers from brittle failure because shear stress leads to formation of amorphous shear bands in which the icosahedral clusters fracture, leading to amorphous regions with higher density than the crystal that results in tension induced cavitation and brittle failure. Based on our previous studies of related systems, we speculated that replacing the C-B-C chains with Si 2 and replacing cage C with Si might reduce or eliminate this amorphous shear band formation responsible for brittle failure, In this paper we consider (B 10 Si 2 )Si 2 , using density functional theory (DFT) to examine its shear deformation. We find that the stress accumulated as shear increases is released by slip of the planes of icosahedra through breaking and then reforming the Si-Si chain bonds without fracturing (B 10 Si 2 ) icosahedra. This is because the (B 10 Si 2 ) icosahedra are more stable than the chain under highly stressed conditions. This chain disruption deformation mode prevents amorphous shear band formation, providing a strategy to dramatically improve the ductility of B 4 C based materials. Our results suggest that making the icosahedra more stable than the chains structure can lead to slipping of the icosahedral planes while avoiding the icosahedral fracturing that leads to brittle failure.

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“…Here we considered the normal compressive pressure beneath the indenter and constrained the ratios of normal stress (σ zz ) to shear stress (σ xz ) as σ zz = σ zx tanΦ where Φ = 68° for a Vickers indentor 8 .…”

Section: Computational Detailsmentioning

confidence: 99%

Nanotwinned Boron Suboxide (B₆O): New Ground State of B₆O

Reddy

Dong

et al. 2016

Nano Lett.

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Nanotwinned structures in superhard ceramics rhombohedral boron suboxide (R-B6O) have been examined using a combination of transmission electron microscopy (TEM) and quantum mechanics (QM). QM predicts negative relative energies to R-B6O for various twinned R-B6O (denoted as τ-B6O, 2τ-B6O, and 4τ-B6O), consistent with the recently predicted B6O structure with Cmcm space group (τ-B6O) which has an energy 1.1 meV/B6O lower than R-B6O. We report here TEM observations of this τ-B6O structure, confirming the QM predictions. QM studies under pure shear deformation and indentation conditions are used to determine the deformation mechanisms of the new τ-B6O phase which are compared to R-B6O and 2τ-B6O. The lowest stress slip system of τ-B6O is (010)/⟨001⟩ which transforms τ-B6O to R-B6O under pure shear deformation. However, under indentation conditions, the lowest stress slip system changes to (001)/⟨110⟩, leading to icosahedra disintegration and hence amorphous band formation.

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Large indentation strain-stiffening in nanotwinned cubic boron nitride

Cited by 111 publications

References 34 publications

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Improved Ductility of B₁₂ Icosahedra-based Superhard Materials through Icosahedral Slip

Nanotwinned Boron Suboxide (B₆O): New Ground State of B₆O

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Large indentation strain-stiffening in nanotwinned cubic boron nitride

Cited by 111 publications

References 34 publications

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Improved Ductility of B12 Icosahedra-based Superhard Materials through Icosahedral Slip

Nanotwinned Boron Suboxide (B6O): New Ground State of B6O

Contact Info

Product

Resources

About

Improved Ductility of B₁₂ Icosahedra-based Superhard Materials through Icosahedral Slip

Nanotwinned Boron Suboxide (B₆O): New Ground State of B₆O