**4. Conclusions**

Stainless steel coatings with varying Ag contents were deposited in inert (Ar) and reactive (Ar and N2) atmospheres by means of magnetron sputtering and their structural, mechanical and tribological properties were studied. The study concludes the following:

BCC and FCC microstructures were exhibited by the coatings deposited in inert and reactive atmospheres, respectively. As for coatings deposited with silver, the FCC structure of silver was also evident. The coatings deposited in a nitrogen atmosphere and with a higher amount of Ag had a smaller crystallite size and higher values of deformation and lattice parameter.

Nanohardness values up to 8 GPa were obtained for the stainless steel coatings, corresponding to a significant increase in the hardness compared to the hardness of the AISI 316L steel used as substrate. The coatings with Ag and deposited in a reactive atmosphere exhibited a higher degree of hardness, which can be attributed to the fact that the use of nitrogen tends to stabilize the austenitic phase of stainless steel and cause an increase in the lattice parameter and the percentage of deformation, due to the supersaturation of nitrogen in the austenitic structure.

The COF in the produced coatings was reduced in comparison with the substrate. In the coatings deposited in a reactive atmosphere, there was a tendency to decrease the COF with an increase in silver content. This behaviour can be attributed to a good solid lubricant, Ag, which allows lubrication of the wear tracks of the film and friction pairs, so that the sliding between the two surfaces tends to decrease the friction coefficient of the coating.

Finally, the wear rates in the produced coatings were reduced in comparison with the substrate, which is associated with the significant increase in the hardness of the coatings. The coatings deposited with lower Ag content (Ar0Ag and ArN0Ag) have a lower value of the wear rate. The decrease in the wear resistance with the increase of Ag is possibly due to an increase in the fragility of the material, loss of adhesion, Ag aggregates, or debris formed on the wear track.

**Author Contributions:** C.L.E.P., A.A.C.R. and J.J.O. conceived and designed the experiments; C.L.E.P. performed the experiments; C.L.E.P., A.A.C.R. and J.J.O. wrote the paper.

**Funding:** This research was funded by National University of Colombia, project "Nanostructured coatings of FCC metallic alloys deposited via sputtering" (37535).

**Conflicts of Interest:** The authors declare no conflict of interest.
