Quasiplastic deformation in shocked nanocrystalline boron carbide: Grain boundary sliding and local amorphization

Abstract

Materials respond to shock in many ways such as plastic flow in metals and amorphization in ceramics. It is very challenging to characterize the deformation mechanisms of ceramics under shock compression due to extreme loading conditions. Here we report the shock response of nanocrystalline boron carbide (n-B4C) using large-scale molecular dynamics simulations with a machine-learning force field. We identify three quasiplastic deformation mechanisms in shocked n-B4C: grain boundary (GB) sliding, intergranular amorphization, and intragranular amorphization. As the deformation mechanism changes from GB sliding to intergranular amorphization at ∼40 GPa, a bilinear Hugoniot behavior occurs, consistent with experimental observations. At higher pressure (>∼100 GPa), intragranular amorphization becomes dominant, causing a complete loss of shear strength. These quasiplastic mechanisms may play an important role in the shock behaviors of ceramics.