Tensile deformation mechanism of amorphous silicon nitride: Insights from molecular dynamics simulations

The molecular dynamics simulations have been carried out to investigate the mechanical behaviors of amorphous silicon nitride under the uniaxial tensile deformation. The amorphous silicon nitride was obtained by the cooling process. The network structure of the sample consists of SiN _x ( x = 3, 4 and 5) units and NSi _y ( y = 2, 3 and 4) linkages. The stress-strain curve of the sample exhibits the elastic and plastic deformation. The Si-N bond lengths are stretched out in the elastic region and the plastic region I. They are shrunk to the initial state in the plastic region II due to the appearance of the large clusters which contain the overlapping big simplexes with the R _S ≥ 2.4 Å. These big simplexes tend to appear at the shear transformation zones in the elastic region. These shear transformation zones tend to form the shear band inclined 45° with the tensile direction. The big simplexes grow and coalesce along the shear band in the plastic region I. In the plastic region II, the clusters of big simplexes grow in the shear band, causing the crack propagation across the sample.