Characterization of the 3-D amorphized zone beneath a Vickers indentation in boron carbide using Raman spectroscopy

Subhash, Ghatu; Ghosh, Dipankar; Blaber, Justin A.; Zheng, James; Halls, Virginia; Masters, Karl

doi:10.1016/j.actamat.2013.03.028

Cited by 48 publications

(58 citation statements)

References 28 publications

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“…2b). These characteristic Raman bands indicate the formation of amorphous B 4 C caused by the indentation, in agreement with previous observations of amorphous B 4 C in single and polycrystalline B 4 C ceramics 14,16,17,19 . ABF-STEM of amorphous shear bands.…”

Section: Resultssupporting

confidence: 80%

“…Raman spectroscopy of amorphous B 4 C. In this study, the amorphous B 4 C was introduced by a nanoindentation experiment 14,16,17,19 . Figure 2 shows the representative Raman spectra acquired from the pristine and residual indented regions of B 4 C. The spectrum of the pristine B 4 C displays characteristic Raman peaks at 270, 320, 481, 531, 728, 830, 1,000 and 1,088 cm À 1 assigned to crystalline B 4 C (refs 24,25), A weak band at 1,580 cm À 1 has been attributed to the presence of a small fraction of graphitic carbon in sintered microcrystalline B 4 C (refs 7,16) (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Diamond anvil cell experiments suggested that the local amorphization of B 4 C, associated with non-hydrostatic stress states, takes place during unloading from a pressure above a critical value of B26 GPa 13 . In addition to shock loading and diamond anvil cell experiments, the amorphization has also been found when B 4 C is subjected to indentation and mechanical scratching [14][15][16][17] . These experimental observations demonstrated that the amorphous shear bands are the dominant deformation and failure modes of B 4 C at room temperature.…”

mentioning

confidence: 99%

“…These experimental observations demonstrated that the amorphous shear bands are the dominant deformation and failure modes of B 4 C at room temperature. On the basis of computer simulations and spectroscopic investigations, several controversial models have been proposed to explain the formation of amorphous shear bands in the super-hard material 1,13,14,[16][17][18][19][20][21] . Nevertheless, the formation mechanisms of the amorphous shear bands still remain intensely debated owing to the lack of direct experimental observation with a sufficient spatial resolution to reveal the detailed structure of the amorphous bands.…”

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Atomic structure of amorphous shear bands in boron carbide

et al. 2013

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Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

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Section: Resultssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Atomic structure of amorphous shear bands in boron carbide

et al. 2013

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“…However, because the loading history of these fragments is unknown, its effect on the observed microstructure is not understood. Additionally, although the more well-defined loading conditions associated with quasi-static diamond-anvil cell (15) and nanoindentation (16,17) experiments have provided greater insight into amorphization of boron carbide, they do not address the regime of high strain rate.…”

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Directional amorphization of boron carbide subjected to laser shock compression

Zhao

Kad

Remington

et al. 2016

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

109

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Solid-state shock-wave propagation is strongly nonequilibrium in nature and hence rate dependent. Using high-power pulsed-laserdriven shock compression, unprecedented high strain rates can be achieved; here we report the directional amorphization in boron carbide polycrystals. At a shock pressure of 45∼50 GPa, multiple planar faults, slightly deviated from maximum shear direction, occur a few hundred nanometers below the shock surface. High-resolution transmission electron microscopy reveals that these planar faults are precursors of directional amorphization. It is proposed that the shear stresses cause the amorphization and that pressure assists the process by ensuring the integrity of the specimen. Thermal energy conversion calculations including heat transfer suggest that amorphization is a solid-state process. Such a phenomenon has significant effect on the ballistic performance of B 4 C.oron carbide is one of the hardest materials on earth while extremely lightweight, making it excellent for ballistic protection applications such as body armor (1-6). Thus, its dynamic behavior under impact/shock loading has been the subject of intensive studies for decades (1,(5)(6)(7)(8)(9)(10)(11)(12)(13). It is known that boron carbide undergoes an abrupt shear strength drop at a critical shock pressure around 20∼23 GPa, suggesting a deteriorated penetration resistance (8). Based on similar observations in geological materials (5), Grady (7) hypothesized that this was caused by localized softening mechanisms such as shear localization and/or melting. Examining fragments collected from a ballistic test using transmission electron microscopy (TEM), Chen et al. (14) were the first to identify localized amorphization in boron carbide, which appeared to be aligned to certain crystallographic planes. However, because the loading history of these fragments is unknown, its effect on the observed microstructure is not understood. Additionally, although the more well-defined loading conditions associated with quasi-static diamond-anvil cell (15) and nanoindentation (16, 17) experiments have provided greater insight into amorphization of boron carbide, they do not address the regime of high strain rate.The laser shock experimental technique offers promise in bridging the gaps of the previous experiments by enabling boron carbide to be shock compressed under controlled and prescribed uniaxial strain loading conditions and then recovered for postshock characterization by TEM. To ensure the integrity of the specimen, the duration of the stress pulse should be smaller than the characteristic time for crack propagation which is typically on the microsecond scale [limited by Rayleigh wave speed (18)]. Traditional dynamic loading methods such as plate impact and split Hopkinson bar cannot deliver the strain rates required because the stress pulses of both techniques occur on microsecond time scales. Therefore, brittle solids such as B 4 C will fail catastrophically by crack nucleation, propagation, and coalescence (19). To solve this ch...

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Dynamic Deformation of Icosahedral Boron‐Based Ceramics

2021

Dynamic Response of Advanced Ceramics

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Characterization of the 3-D amorphized zone beneath a Vickers indentation in boron carbide using Raman spectroscopy

Cited by 48 publications

References 28 publications

Atomic structure of amorphous shear bands in boron carbide

Atomic structure of amorphous shear bands in boron carbide

Directional amorphization of boron carbide subjected to laser shock compression

Dynamic Deformation of Icosahedral Boron‐Based Ceramics

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