Molecular Dynamics Simulation of Deposition and Nanoindentation in SiN_<i>x</i>/BN_<i>y</i> 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. SiNx/BNy PNCs consisting of alternated SiNx and BNy layers exhibit favorable mechanical and optical properties. The mechanical properties of the SiNx/BNy PNCs are related to the thicknesses of the SiNx and BNy layers, but the strengthening mechanism is not clear. In this study, molecular dynamics (MD) simulations are used to model the deposition process of the SiNx/BNy PNCs, achieving SiNx/BNy 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 SiNx/BNy PNCs models, MD simulations are used to study the nanoindentation process. The simulations revealed that, for a fixed SiNx thickness of 2.4 nm, the coating hardness is dependent on the thickness of the BNy 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 SiNx 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 BNy layers fail to form distinct interfaces with SiNx, while thicker BNy layers enhance the interfacial obstruction to strain propagation. Conversely, when the BNy layer becomes excessively thick, the mechanically weaker BNy layer undergoes significant strain due to compression from the overlying SiNx 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.