**4. Conclusions**

• The Cu/MoS2 composite coatings with various Cu contents were prepared by magnetron sputtering and the tribological properties were tested at room temperature. The Cu10 coating had the lowest friction coefficient among all Cu/MoS2 coatings, whereas the friction coefficient of the Cu5Al5 coating was the lowest in all Cu-Al/MoS2 coatings. The average friction coefficients of the Cu10 and the Cu5Al5 coatings were both lower than the pure MoS2 coating. The abrasion resistance of the coatings co-doped with Cu and Al was significantly enhanced through wear rate qualitative comparison. It was very probable that the γ2-Cu9Al4 phase in the co-sputtered Cu-Al/MoS2 coatings improved the wear resistance.


**Acknowledgments:** The authors gratefully acknowledge the financial research support of the Project of New Century 551 Talent Nurturing in Wenzhou (2016 No.30). The authors would also like to thank the Zhejiang Provincial Key Laboratory for Cutting Tools for offering access to their instruments and expertise, the Zhejiang Provincial Key Laboratory of Carbon Materials for providing the sample preparation equipment along with the SEM and XRD facilities, as well as the Wenzhou City Key Laboratory of Materials Forming and Tooling Technology for offering the MFT-4000 device and surface roughness testing equipment.

**Author Contributions:** M.C. and W.W. conceived and designed the experiments; M.C., L.Z. and L.W. performed the experiments; M.C. analyzed the data; M.C., L.Z. and W.W. cooperatively wrote this article.

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