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 -Si3N4 films using a rigid indenter are reported. Local pressure distributi ons and configuration images of the plastically deformed region are present ed. Residual tensile pressures correspond to voids and cracks that separate regions of compacted, plastically deformed material and elastically recove red crystalline material. Structural analysis shows that pile-up material o n the surface and deformed material under the indenter is amorphous. With t his indenter geometry, Si3N4 deforms primarily by amorphization, which is a rrested by cracking at the indenter corners and piling-up of material along the indenter sides. Indentation fracture exhibits anisotropic behavior con sistent with the orientation-dependent fracture toughness values. (C) 2000 American Institute of Physics. [S0003- 6951(00)01048-2].