Improved Ductility of B12 Icosahedra-based Superhard Materials through Icosahedral Slip

Abstract

Boron carbide (B4C) is superhard but suffers from brittle failure because shear stress leads to the formation of amorphous shear bands in which the icosahedral clusters fracture, leading to amorphous regions with higher density than the crystal that results in tension-induced cavitation and brittle failure. On the basis of our previous studies of related systems, we speculated that replacing the C–B–C chains with Si2 and replacing cage C with Si might reduce or eliminate this amorphous shear band formation responsible for brittle failure. We consider (B10Si2)Si2, using density functional theory to examine its shear deformation. We find that the stress accumulated as shear increases is released by slip of the planes of icosahedra through breaking and then reforming the Si–Si chain bonds without fracturing (B10Si2) icosahedra. This is because the (B10Si2) icosahedra are more stable than the chain under highly stressed conditions. This chain disruption deformation mode prevents amorphous shear band formation...