Microstructural evolution and tribological behavior of Mo–Cu–N coatings as a function of Cu content

Ternary Mo–Cu–N coatings with various Cu contents were deposited on Si wafers and AISI 304 substrates by magnetron co-sputtering from two elemental targets of Mo and Cu in Ar–N2 gas mixtures. The influence of copper content was investigated with regard to the microstructure, morphology, and tribological properties of these coatings. The results indicated that the Mo–Cu–N coatings exhibited face-centered-cubic B1-MoN phase structure. No diffraction peaks of Cu phase appeared in the coatings with Cu content below 11 at.%. The copper segregated in the amorphous inter-granular phase in the coatings. Incorporation of Cu into the growing Mo–N coating led to grain refinement. The average friction coefficient of the Mo–Cu–N coatings decreased from 0.40 to 0.21 with increasing Cu content up to 11 at.% due to formation of lubricious oxides of CuMoO4.