Transgranular amorphous shear band formation in polycrystalline boron carbide

Intragranular failure plays an important role in the failure process of superhard nanocrystalline ceramics. But the atomistic deformation mechanisms leading to intragranular failure have not been well established. Here we performed large-scale reactive force field (ReaxFF) reactive molecular dynamics (RMD) simulations on the finite shear deformation of nanocrystalline boron carbide (n-B₄C) with a grain size of 9.74 »nm. We find that intragranular amorphization initiates from grain boundaries (GBs) and propagates along the rhombohedral (011)<21̄1̄> slip system. To illustrate the atomic mechanism of amorphous shear band formation along this slip system, we combined density functional theory (DFT) and RMD simulations on the shear deformation of single crystal B₄C. These simulations displayed that the dislocation nucleation occurs along this slip system, accompanied with bond breaking of intraicosahedral bonds within B₁₁C cage. This leads to the amorphous shear band formation under the applied shear deformation. Our simulations suggest that the coupling of dislocation nucleation and GB sliding leads to the intragranular amorphous shear band formation and may leads to the intragranular failure in n-B₄C.