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Abstract The high strength of boron carbide (B4C) is essential in its engineering applications such as wear‐resistance and body armors. Here, by employing density functional theory simulations, we demonstrated that the strength of B4C can be enhanced by doping lithium to boron‐rich boron carbide (B13C2) to form r‐LiB13C2. The bonding analysis on r‐LiB13C2indicates that the electron counting rule (or Wade's rule) is satisfied in r‐LiB13C2whose formula can be written as r‐Li+(B12)2‐(CB+C). The shear deformation on r‐LiB13C2indicates that its ideal shear strength is larger than that of B4C because of the existing of Li dopant. The failure process of r‐LiB13C2under ideal shear deformation initiates from breaking the icosahedral‐icosahedral B‐B bonds. Then these B atoms react with the middle B in the C‐B‐C chain, resulting in the disintegration of icosahedral clusters and brittle failure. More interesting, the nanotwinned r‐LiB13C2is even stronger than r‐LiB13C2because of the directional nature of covalent bonding at the twin boundaries. This suggests that the nanotwinned r‐LiB13C2has a significant enhanced strength compared to B4C. Our simulation results illustrate the deformation mechanism of Li‐doped boron carbide and its nanotwinned microstructure. We proposed to improve the strength of boron carbide by doping Li into B13C2and increasing its twin densities.
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First principles predicting enhanced ductility of boride carbide through magnesium microalloying
Abstract The low fracture toughness of strong covalent solids prevents them from wide engineering applications. Microalloying metal elements into covalent solids may lead to a significant improvement on mechanical properties and drastical changes on the chemical bonding. To illustrate these effects we employed density functional theory (DFT) to examine the bonding characteristic and mechanical failure of recently synthesized magnesium boride carbide (Mg3B50C8) that is formed by adding Mg into boron carbide (B4C). We found that Mg3B50C8has more metallic bonding charterer than B4C, but the atomic structure still satisfies Wade's rules. The metallic bonding significantly affects the failure mechanisms of Mg3B50C8compared with B4C. In Mg3B50C8, the B12icosahedral clusters are rotated in order to accommodate to the extensive shear strain without deconstruction. In addition, the critical failure strength of Mg3B50C8is slightly higher than that of B4C under indentation stress conditions. Our results suggested that the ductility of Mg3B50C8is drastically enhanced compared with B4C while the hardness is slightly higher than B4C.
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- Award ID(s):
- 1727428
- PAR ID:
- 10459900
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 102
- Issue:
- 9
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 5514-5523
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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