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First principles predicting enhanced ductility of boride carbide through magnesium microalloying
Author(s) -
Tang Bin,
He Yi,
Goddard William A.,
An Qi
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16383
Subject(s) - materials science , ductility (earth science) , boron carbide , carbide , covalent bond , boride , magnesium , metallurgy , fracture toughness , chemical bond , metal , crystallography , chemistry , creep , organic chemistry
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 (Mg 3 B 50 C 8 ) that is formed by adding Mg into boron carbide (B 4 C). We found that Mg 3 B 50 C 8 has more metallic bonding charterer than B 4 C, but the atomic structure still satisfies Wade's rules. The metallic bonding significantly affects the failure mechanisms of Mg 3 B 50 C 8 compared with B 4 C. In Mg 3 B 50 C 8 , the B 12 icosahedral clusters are rotated in order to accommodate to the extensive shear strain without deconstruction. In addition, the critical failure strength of Mg 3 B 50 C 8 is slightly higher than that of B 4 C under indentation stress conditions. Our results suggested that the ductility of Mg 3 B 50 C 8 is drastically enhanced compared with B 4 C while the hardness is slightly higher than B 4 C.