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 Mg3B50C8 has more metallic bonding charterer than B4C, but the atomic structure still satisfies Wade's rules. The metallic bonding significantly affects the failure mechanisms of Mg3B50C8 compared with B4C. In Mg3B50C8, the B12 icosahedral clusters are rotated in order to accommodate to the extensive shear strain without deconstruction. In addition, the critical failure strength of Mg3B50C8 is slightly higher than that of B4C under indentation stress conditions. Our results suggested that the ductility of Mg3B50C8 is drastically enhanced compared with B4C while the hardness is slightly higher than B4C.

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.…”

Models for the behavior of boron carbide in extreme dynamic environments

“…Our studies of brittleness in B 4 C showed that cracking across grains leads to amorphization 24 and we showed that very small grains lead to grain boundaries that direct shear along these boundaries 28 . This was studied in depth in collaboration with Lasalvia 34 . Interestingly, we found that microalloying with Mg also leads to enhanced ductility 35 .…”

“…28 This was studied in depth in collaboration with Lasalvia. 34 Interestingly, we found that microalloying with Mg also leads to enhanced ductility. 35 This has not yet been tested experimentally.…”

Strengthening boron carbide by doping Si into grain boundaries

“…Several approaches, such as microalloying, [12][13][14][15][16] stoichiometry control, [17][18][19] and addition of a second phase, [20][21][22] have been proposed to mitigate amorphous shear band formation. For microalloying, both non-metal dopants (P 23 and Si 24 ), as well as metal dopants (Li, 14,15 Mg, 12,16 and Ti 13 ) may decrease amorphization in B 4 C. Both experimental and theoretical studies have suggested that boron enrichment is helpful to mitigate amorphization. [17][18][19] Moreover, the addition of the second phase, such as SiC 25 and TiB 2 26 has been shown to improve the fracture toughness of B 4 C. Among these approaches, grain-boundary (GB) engineering is promising.…”