Diffusion of silver in titanium nitride: Insights from density functional theory and molecular dynamics

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The use of self-lubricating titanium nitride and silver (TiN(Ag)) nanocomposite coatings is a promising way to reduce the wear of tools employed dry machining operations for hard-to-cut materials/alloys. To achieve an optimal performance, the Ag diffusion within the matrix needs to be carefully controlled, and its mechanisms clearly understood. In this paper we use density functional theory calculations to investigate Ag-related point defects, adhesion energies and Ag diffusion energy barriers in TiN bulk, surfaces and grain boundaries. Classical molecular dynamics simulations have been performed on TiN(Ag) systems using a hybrid MEAM/Mie force field, to understand the relative importance of the different diffusion processes. Our results show that the main Ag transport mechanism in TiN(Ag) nanocomposites is the surface diffusion occurring along intergranular spaces.