Tribology and wettability of nano-machined silicon rough surfaces

1 – Introduction The more and more pressing demand for eliminating liquid lubricants in mechanical devices, due to their environmental costs, represents an important challenge for the tribological community. Low-friction coatings, like layered materials (graphite, Mo2S), soft metals (Ag, Au), non-layered metal oxides (MoO3, V2O5), can substitute liquid lubricants, but presently they are characterized by poor mechanical properties. On the other hand, hard ceramic coatings, like CrN, TiN, TiCN, TiAlN, have been studied for the last three decades for their high hardness, chemical inertness, high oxidation resistance and low wear rate. The aim of our study is to couple the properties of hard ceramics with those of soft metals low friction coatings. The nanostructuring of CrN-Ag ternary coating represents an appealing solution. 2 – Main Body of Text We studied the tribo-mechanical properties of CrN-Ag ternary coatings, where Ag clusters are dispersed in a CrN thick film. Some preliminary tests were also performed on a similar system, composed by Ag/CrN multilayers. CrN-Ag composite coatings were deposited on Si(100) and on a steel (20MnCr5) using PVD Magnetron Sputtering in a mixed N2+Ar atmosphere (P=5mtorr), with temperature ranging from RT to 500°. Structure, composition and morphology of both systems were characterized by Auger Electron Spectroscopy, X-rays diffraction and cross sectional analysis (depth-profiling AES, FIB cross section). The co-deposition of CrN and Ag in N2 atmosphere leads to the formation of a composite nanostructured coating, where Ag clusters behave as solid lubricant in the hard CrN bulk. Tribo-mechanical properties were measured with a ball-on-disc tribometer and a Berckovich nanoindenter. 3 – Conclusion By tuning the preparation conditions we were able to control the size, the distribution and the self organization of Ag nanoclusters in the CrN matrix, thus controlling frictional behavior.