While nanocrystalline diamond is quickly becoming one of the most widely studied nanomaterials, achieving a large fraction of diamond nanoparticles in a polymer coating has been an unresolved problem. In this work, polymer nano- and microfibers containing high loadings of 5 nm diamond particles (up to 80 wt % in polyacrylonitrile and 40% in polyamide 11) have been demonstrated using electrospun nanofibers as a delivery vehicle. The electrospun nanofibers with a high load of nanodiamond in the polymers were fused into thin transparent films, which had high mechanical properties; an improvement of 4 times for the Young's modulus and 2 times for the hardness was observed already at 20% nanodiamond in polyamide 11. These films can provide UV protection and scratch resistance to a variety of surfaces, especially in applications where a combination of mechanical, thermal, and dielectric properties is required.

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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...

The well-documented formation of amorphous bands in boron carbide (B 4 C) under contact loading has been identified in the literature as one of the possible mechanisms for its catastrophic failure. To mitigate amorphization, Si-doping was suggested by an earlier computational work, which was further substantiated by an experimental study. However, there have been discrepancies between theoretical and experimental studies, about Si replacing atom/s in B 12 icosahedra or the C-B-C chain. Dense single phase Si-doped boron carbide is produced through a conventional scalable route. A powder mixture of SiB 6 , B 4 C, and amorphous boron is reactively sintered, yielding a dense Si-doped boron carbide material.A combined analysis of Rietveld refinement on XRD pattern coupled with electron density difference Fourier maps and DFT simulations were performed in order to investigate the location of Si atoms in boron carbide lattice. Si atoms occupy an interstitial position, between the icosahedra and the chain. These Si atoms are bonded to the chain end C atoms and result in a kinked chain. Additionally, these Si atoms are also bonded to the neighboring equatorial M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT2 B atom of the icosahedra, which is already bonded to the C atom of the chain, forming a bridge like geometry. Si atoms are found to reside around the chain, resulting in a kinked chain. These Si atoms lie close to boron atom of the neighboring icosahedra. Owing to this bonding, distance suggests weak bonding and Si is anticipated to stabilize the icosahedra through electron donation, which is expected to help in mitigating stress-induced amorphization. Possible supercell structures are suggested along with the most plausible structure for Si-doped boron carbide.