Cr2N0.62-11Ag adaptive nanocomposite thin films: Transport of Ag solid lubricant during annealing in a closed-air atmosphere

Cr2N0.62-11Ag adaptive nanocomposite thin films were grown by reactive magnetron sputtering at a temperature of 500 °C, with the as-deposited films then annealed at temperatures of 300-500 °C in a closed-air atmosphere for up to 24 h. Structural changes were evaluated by scanning electron microscopy, Auger electron spectroscopy and X-ray diffraction. During annealing, silver first diffused to the free surface, thus increasing the surface population density of Ag particles, with maximum Ag diffusion detected after 0.5 and 4 h of annealing at temperatures of 400 and 300 °C, respectively. Subsequently, the population density of silver particles decreased, with this decrease most emphatic after annealing at 500 °C, followed by a coarsening of the Ag particles. These variations are discussed and explained as follows: At low temperatures, no oxide layer is formed in the early stages of annealing. Hence, Ag transport towards the surface is steady and the surface population density of Ag particles increases. In contrast, oxide formation, which is pronounced at either higher temperatures or during longer duration annealing, hinders Ag transport and consequently leads to a reduction in the population density of Ag particles due to their sublimation. The obtained results indicate that Cr2N0.62-11Ag films are less amenable to oxidation and associated microstructural alteration than Cr2N0.61-7Ag films.