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Thin films of Mo2N/Ag nanocomposite

Time:2019-11-14 19:21:53  From:  Author:

 

Although nitrides of copper (Cu3N and CuN3) and silver (AgN3) are known, their thermal stability is very limited and they easily decompose into free metals. High hardness and long term stability of the nanostructure have been reported for nitride containing composites such as ZrN/Cu, ZrTiN/Cu , CrN/Cu, CrN/Ag, TiN/Cu, TiN/Ag, Mo2N/Cu and Mo2N/Ag as well as carbide/silver (TiC/Ag, WC/Ag) combinations. The Mo2N thin film coatings oxidize to the lamellar oxide MoO3 playing a key lubricating role in high temperature(HT) friction process on that nitride. An addition of silver to molybdenum oxide leads to the synthesis of low-melting silver molybdates, exhibiting low friction in the wide temperature range. Thus, the silver doped molybdenum nitride coatings, beside their composite nanostructure, are expected to show interesting HT tribological properties. Mo2N/Ag nanocomposite thin film coatings have been deposited by doublesource, reactive magnetron sputtering. An addition of silver up to 2.5 at.% led to the slight increase of hardness (from 24 to 29GPa) induced by the nitride crystallite size refinement to about 10nm. At higher Ag concentrations, the composite hardness drops down to 7GPa. The silver addition induces a distortion of the γ-Mo2N nitride lattice and consequently leads to the appearance of tetragonal β-Mo2N phase. Free metallic silver emerges in diffraction patterns when its concentration approaches 15 at.%.The positive influence of silver on tribological behavior of studied coatings has been observed during high temperature tests. The optimum content of Ag is slightly above 6 at.%. The hardness of composite at this Ag concentration is still sufficiently high (about 20GPa), whereas the friction coefficient is clearly lowered.

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