Mo2N/Cu thin films — the structure, mechanical and tribological properties

Thin, nanocomposite films of copper doped molybdenum nitride (γ-Mo2N) were deposited by double source, reactive magnetron sputtering. Their structure, microhardness and tribological properties in the wide temperature range (20–400 °C) were studied. An addition of copper results in the refinement of nitride crystallites from 12 nm for pure Mo2N to the level of 6 nm for copper content close to 22 at.%. At low copper concentrations (around 1–3 at.%) slight increase of microhardness has been observed. Free, metallic copper phase has not been identified in diffraction patterns up to the highest concentrations (22 at.%). Most probably copper is dispersed at the grain boundaries in form of nano-clusters with the size below the X-ray diffraction limit.Tribological properties of molybdenum nitride films depend on copper content. It is particularly visible during 100 °C sliding tests. At that temperature the wear rate decreased significantly for copper concentration higher than 6 at.%. Simultaneously, the oxidation rate of this nanocomposite material seems to be promoted by copper. However, the oxidation product containing MoO2, MoO3 and traces of copper molybdate CuMoO4, shows much better adhesion to the native coating than pure molybdenum oxide.