Structure mechanical properties, and dynamic fracture in nanophase silicon nitride via parallel molecular dynamics

Million-atom molecular-dynamics (MD) simulations are performed to study the structure, mechanical properties, and dynamic fracture in nanophase Si₃N₄. We find that intercluster regions are highly disordered: 50% of Si atoms in intercluster regions are three-fold coordinated. Elastic moduli of nanophase Si₃N₄ as a function of grain size and porosity are well described by a multiphase model for heterogeneous materials. The study of fracture in the nanophase Si₃N₄ reveals that the system can sustain an order-of-magnitude larger external load than crystalline Si₃N₄. This is due to branching and pinning of the crack front by nanoscale microstructures.