Dynamic Indentation Response of Fine‐Grained Boron Carbide

Ghosh, Dipankar; Subhash, Ghatu; Sudarshan, T. S.; Radhakrishnan, R.; Gao, X.-L.

doi:10.1111/j.1551-2916.2007.01652.x

Cited by 110 publications

(89 citation statements)

References 48 publications

(89 reference statements)

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“…The indentation size effect is probably associated with the strain gradient underneath indenter, which may be different from the one in metals caused by geometrical necessary dislocations. The H and E values of n-B 4 C are comparable to those of microcrystalline B 4 C at similar loads [17][18][19][20] , but less than those of single-crystal B 4 C (ref. 21).…”

Section: Resultsmentioning

confidence: 93%

“…The crack length c is measured from the indentation centre to the tip of the emanated cracks as shown in the Fig. 2c), more than 75% higher than that of microcrystalline B 4 C (refs [18][19][20]24,25). Figure 2d shows the typical Raman spectra collected from the pristine and residual indents at different loading forces.…”

Section: Mechanical Properties and Raman Spectroscopy Analysismentioning

confidence: 97%

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Enhanced mechanical properties of nanocrystalline boron carbide by nanoporosity and interface phases

et al. 2012

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Ceramics typically have very high hardness, but low toughness and plasticity. Besides intrinsic brittleness associated with rigid covalent or ionic bonds, porosity and interface phases are the foremost characteristics that lead to their failure at low stress levels in a brittle manner. Here we show that, in contrast to the conventional wisdom that these features are adverse factors in mechanical properties of ceramics, the compression strength, plasticity and toughness of nanocrystalline boron carbide can be noticeably improved by introducing nanoporosity and weak amorphous carbon at grain boundaries. Transmission electron microscopy reveals that the unusual nanosize effect arises from the deformation-induced elimination of nanoporosity mediated by grain boundary sliding with the assistance of the soft grain boundary phases. This study has important implications in developing high-performance ceramics with ultrahigh strength and enhanced plasticity and toughness.

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Section: Resultsmentioning

confidence: 93%

Section: Mechanical Properties and Raman Spectroscopy Analysismentioning

confidence: 97%

Enhanced mechanical properties of nanocrystalline boron carbide by nanoporosity and interface phases

et al. 2012

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“…This loss is attributed to the formation of nanoscale amorphous shear bands (11). The shear amorphization of boron carbide has been confirmed by indentation experiments (12)(13)(14)(15)(16), but a fundamental understanding of the mechanism underlying it has not been fully established. It has been suggested that local shear first breaks the weaker chains and then, displaces and ruptures the stronger icosahedra (16), but recent quantum mechanics (QM) simulations attribute the instability to disintegration of the icosahedra (17,18).…”

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confidence: 99%

Breaking the icosahedra in boron carbide

Xie

Sato

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Findings of laser-assisted atom probe tomography experiments on boron carbide elucidate an approach for characterizing the atomic structure and interatomic bonding of molecules associated with extraordinary structural stability. The discovery of crystallographic planes in these boron carbide datasets substantiates that crystallinity is maintained to the point of field evaporation, and characterization of individual ionization events gives unexpected evidence of the destruction of individual icosahedra. Statistical analyses of the ions created during the field evaporation process have been used to deduce relative atomic bond strengths and show that the icosahedra in boron carbide are not as stable as anticipated. Combined with quantum mechanics simulations, this result provides insight into the structural instability and amorphization of boron carbide. The temporal, spatial, and compositional information provided by atom probe tomography makes it a unique platform for elucidating the relative stability and interactions of primary building blocks in hierarchically crystalline materials.bond dissociation | laser-assisted atom probe tomography | ab initio molecular dynamics | multiple hits I cosahedra are commonly observed polyhedra in nature and can be found in a wide variety of molecules, viruses, minerals, and ceramics (1-4). The architecturally efficient icosahedral geometry and tight covalent bonding result in an unusually stable atomic configuration and in many cases, extraordinary properties. The prodigious structural stability, rigidity, and strength of C 60 nearly spherical fullerene molecules (Bucky balls) are well-documented and have received considerable attention (5). Elemental boron and boron-based ceramics also form nearly spherical icosahedra (3,4,6), and the extreme hardness of these borides has been attributed to the presence of these icosahedra. In the case of boron carbide, one of the hardest structural ceramics, B 12 or B 11 C icosahedra are stacked with rhombohedral symmetry and connected by three atom chains (Fig. 1A) (3, 6).For boron carbide, the relative bond strength between the atoms in the icosahedra and chains is still being debated, but the icosahedra are generally thought to be very strong and stable because of their near-spherical shape and the highly delocalized fullerene-like intraicosahedral sp 2 bonds (3, 7-10). As a result of its high hardness, boron carbide is an excellent candidate for use in personal body armor; however, it undergoes a dramatic loss of ballistic performance in high-energy impacts. This loss is attributed to the formation of nanoscale amorphous shear bands (11). The shear amorphization of boron carbide has been confirmed by indentation experiments (12-16), but a fundamental understanding of the mechanism underlying it has not been fully established. It has been suggested that local shear first breaks the weaker chains and then, displaces and ruptures the stronger icosahedra (16), but recent quantum mechanics (QM) simulations attribute the instability to disinte...

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“…The dynamic indentations were conducted using a dynamic indentation hardness tester described in earlier publications by Subhash and co-workers. [16,[19][20][21] The duration of dynamic loading was around 100 ls. The strain rate of indentation was estimated to be above 1000/s.…”

Section: Experimental Methodsmentioning

confidence: 99%

Shear Band Patterns in Metallic Glasses under Static Indentation, Dynamic Indentation, and Scratch Processes

Subhash

Zhang

2007

Metall Mater Trans A

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The deformation structure in terms of shear band patterns in bulk metallic glasses (BMGs) under static indentation, dynamic indentation, and dynamic scratch tests has been investigated. The evolved shear band patterns appear to be a strong function of loading rate, although the plastic regions beneath the loading surface have similarities in shape irrespective of loading type. Comparison of currently available modeling estimates with experimental measurements has revealed that these models predict the plastic zone size reasonably well at low loads but deviate considerably at higher loads. The variation in spacing of shear bands is rationalized on the basis of the shear displacement accommodated by the shear bands formed under different loading rates, which results from a proposed shear-band formation mechanism based on the momentum diffusion model.

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Dynamic Indentation Response of Fine‐Grained Boron Carbide

Cited by 110 publications

References 48 publications

Enhanced mechanical properties of nanocrystalline boron carbide by nanoporosity and interface phases

Enhanced mechanical properties of nanocrystalline boron carbide by nanoporosity and interface phases

Breaking the icosahedra in boron carbide

Shear Band Patterns in Metallic Glasses under Static Indentation, Dynamic Indentation, and Scratch Processes

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