Million atom molecular dynamics simulation of nanophase silicon nitride

Structural correlations and dynamic fracture in nanocluster-assembled silicon nitride are investigated with molecular-dynamics (MD) simulations involving 1.08 million particles. These simulations reveal that the consolidated nanophase Si3N4 has highly disordered intercluster regions that contain 50% under-coordinated atoms. Amorphous interfacial regions deflect cracks and give rise to local crack branching. These dissipative mechanisms enable the nanophase system to sustain an order-of-magnitude larger external strain than crystalline Si3N4. The morphology of fracture surfaces in nanophase Si3N4 is also determined. The MD results for roughness exponents are very close to experimental values even though the materials and length scales are very different.