Mechanical properties of B12-based orthorhombic metal carboborides MC2B12 (M= Mg, Ca, Sr, Sc, Y). A first principle study

Structural and mechanical properties of B 12 -based orthorhombic metal carboborides are studied on the basis of first principle DFT approach. The simulations predict the existence of a new family of phases of the composition MC 2 B 12 (M=Mg, Ca, Sr, Sc, Y) with similar structure and space symmetry Imma. It has been found that the predicted phases are thermally and dynamically stable and have considerably better mechanical properties as compared to the reference compound AlMgB 14 . The respective calculated isotropic elastic moduli and Vickers hardness are significantly higher (G∼ 230–250, E∼530–550, and H v ∼35–55 GPa). These conclusions were confirmed by direct calculations of shear strength for the above phases, which demonstrated the increase of 30–50 % in different directions. The enhanced mechanical characteristics of the MgC 2 B 12 -based phases make them promising for creating novel superhard materials. • Orthorhombic B 12 -based metal carboborides represent a family of hard phases. • Shear strength is enhanced with replacing inter-icosahedral boron atoms by carbon. • Elastic failure is associated with breaking inter-layer B-B or C-C bonds. • Dynamical stability is established by Born-Oppenheimer molecular dynamics.