Amorphization and anisotropic fracture dynamics during nanoindentation of silicon nitride: A multimillion atom molecular dynamics study

Molecular dynamics simulations of nanoindentation of 10 million atom $\alpha {\mathrm{-Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}}$ films using a rigid indenter are reported. Local pressure distributions and configuration images of the plastically deformed region are presented. Residual tensile pressures correspond to voids and cracks that separate regions of compacted, plastically deformed material and elastically recovered crystalline material. Structural analysis shows that pile-up material on the surface and deformed material under the indenter is amorphous. With this indenter geometry, ${\mathrm{Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}}$ deforms primarily by amorphization, which is arrested by cracking at the indenter corners and piling-up of material along the indenter sides. Indentation fracture exhibits anisotropic behavior consistent with the orientation-dependent fracture toughness values.