Molecular Dynamics Simulation of Deposition and Nanoindentation in SiN_x/BN_y Amorphous Periodical Nanolayered Coatings: Insights into Growth and Strengthening Mechanisms

Deposition of periodical nanolayered coatings (PNCs) using magnetron sputtering is a practical approach to strengthening amorphous coatings. SiN x /BN y PNCs consisting of alternated SiN x and BN y layers exhibit favorable mechanical and optical properties. The mechanical properties of the SiN x /BN y PNCs are related to the thicknesses of the SiN x and BN y layers, but the strengthening mechanism is not clear. In this study, molecular dynamics (MD) simulations are used to model the deposition process of the SiN x /BN y PNCs, achieving SiN x /BN y PNC models with different layer thicknesses that align well with experimental observations. The effect of the incident kinetic energy of atoms on the component density is investigated. Based on the established SiN x /BN y PNCs models, MD simulations are used to study the nanoindentation process. The simulations revealed that, for a fixed SiN x thickness of 2.4 nm, the coating hardness is dependent on the thickness of the BN y layer. When the BN thickness is 0.6 nm, the PNC simulated hardness is 59.7 GPa, which is greater than the hardness of the SiN x one-component coating. When the BN thickness is increased to 1.4 nm, the PNC simulated hardness decreases to 49.8 GPa. This phenomenon can be attributed to the fact that thin BN y layers fail to form distinct interfaces with SiN x, while thicker BN y layers enhance the interfacial obstruction to strain propagation. Conversely, when the BN y layer becomes excessively thick, the mechanically weaker BN y layer undergoes significant strain due to compression from the overlying SiN x layer, leading to enhanced strain propagation and stress concentration, which ultimately reduces the coating’s hardness. Accurate nanoindentation tests validated the simulation results. These findings provide valuable insights into the structural design of PNCs, paving the way for further optimization of their mechanical performance.