Speaker
Description
The nowadays requirements for high-performance materials in aerospace industry pose a challenge in terms of their tooling and machining. A promising way to reduce the wear of cutting tools, thereby extending their lifetimes, is represented by the application of self-lubricating nanocomposite coatings. It has been recently shown that Ag nanoparticles dispersed in a superhard TiSiN matrix are very promising.
In these systems Ag diffuses to the surface within and along the matrix free surfaces and grain boundaries (GB), and the control of the diffusion rate is fundamental to design the coating and optimize its performance. Here, we employed ab-initio calculations and molecular dynamics (MD) simulations to understand the diffusion mechanism of Ag within the nanocomposite coating.
Firstly, the formation energy of Ag-related point defects such as Ag interstitials and substitutions has been calculated using density functional theory (DFT). Potential energy landscapes were obtained for Ag diffusion over TiN and SiN surfaces, as well as for diffusion along grain boundaries.
MD simulations of TiN/Ag systems have been performed, using a hybrid MEAM-Mie forcefield obtained by merging pre-existing ones and adding a Mie term for the Ag-N interaction, with the help of DFT data. Ag diffusion in presence of GBs and surfaces was characterized under different temperature and pressure conditions.
Our results indicate that the diffusion along TiN surfaces is the fastest diffusion mechanism. Diffusion along grain boundaries is slower and directly related to the size of GB. Conversely, bulk diffusion appears extremely slow due to the high interstitial and defect formation energies. Surface defects might act as diffusion traps for Ag.
Our study provides a clear understanding of the Ag transport in TiSiN/Ag nanocomposite coatings, indicating that the correct strategy to control Ag diffusion is to act on the surface diffusion process.
| Speaker Country | Portugal |
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