Locating Si atoms in Si-doped boron carbide: A route to understand amorphization mitigation mechanism

Abstract

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.

First principles predicting enhanced ductility of boride carbide through magnesium microalloying

“…Particularly, previous density functional theory (DFT) studies have suggested that doping Si into B 4 C can significantly enhance the ductility by suppressing the deconstruction of icosahedral clusters. This was validated by a very recent experiment indicating that adding ~1.5at% Si into B 4 C exhibits the mitigation of the amorphous shear band formation . Another DFT study showed that making co‐crystal of B 4 C and B 6 O can suppress the failure mechanism of B 4 C, thereby improving its ductility .…”

“…This was validated by a very recent experiment indicating that adding ~1.5at% Si into B 4 C exhibits the mitigation of the amorphous shear band formation. 14 Another DFT study showed that making co-crystal of B 4 C and B 6 O can suppress the failure mechanism of B 4 C, thereby improving its ductility. 13 In addition, the recent study combining transmission electron microscopy experiments and reactive force field (reaxFF) reactive molecular dynamics simulations indicated that decreasing the grain size to nanoscale in B 4 C facilitates the grain-boundary (GBs) sliding, thus enhancing the ductility of polycrystalline B 4 C. 15 Recently, adding metals into B 4 C has been very attractive because this may drastically change its mechanical, | 5515 TANG eT Al.…”

Strengthening boron carbide through lithium dopant

“…The density functional theory (DFT) study on NiAl alloy has shown that its ductility can be improved by microalloying Cr, Mo, Ti, and Ga elements into the cleavage or slip planes . For superhard materials, it has been demonstrated in both experiment and theory that microalloying Mg and Si in B 4 C can improve its mechanical properties …”

“…41 For superhard materials, it has been demonstrated in both experiment and theory that microalloying Mg and Si in B 4 C can improve its mechanical properties. [42][43][44][45] In this Article, we employed DFT simulations at the Perdew-Burke-Ernzerhof (PBE) functional level 46 to examine the mechanical properties of r-LiB 13 C 2 and how the nanoscale twins affect the mechanical properties. We first examined the single crystal r-LiB 13 C 2 and identified its elastic modulus and failure mechanism under pure shear and indentation stress conditions.…”

The effect of boron and aluminum additions on the microstructure of arc‐melted boron carbide

“…To improve the ballistic performance of boron carbide, amorphization mitigation via chemical alloying was proposed . Such strategy has been proved viable from both simulations and experiments . B 4 C consists of 12‐atom icosahedra (mostly B 11 C) connected via 3‐atom linear chains (eg, ‐CBC‐).…”