Activating Mobile Dislocation in Boron Carbide at Room Temperature via Al Doping.

Dislocation glide, deformation twinning, and phase transition are critical mechanisms resulting in irreversible plastic deformations of materials. Because of the lack of dislocation movement, superhard ceramics generally exhibit brittle failure at room temperature. Here, by employing molecular dynamics simulations using a machine-learning force field, we reveal several plastic deformation mechanisms in superhard boron carbide as a small amount of aluminum (Al) is doped. Under shear deformation, dislocation nucleation and glide occur in Al-doped boron carbide (B_{12}-CAlC) due to the breakage of weakened chain bonds rather than the disintegration of icosahedral clusters. The dislocation activities then cause twin boundaries to migrate, thereby mitigating amorphization and enhancing ductility. Furthermore, the mobile dislocation with the Burgers vector of b=⟨11[over ¯]0⟩{111} is observed in the tensile nanopillar, which is well consistent with the experiment. This Letter demonstrates that mobile dislocation could be activated in superstrong covalent materials through a simple doping strategy.