*Article* **Tribological Properties of New Cu-Al/MoS 2 Solid Lubricant Coatings Using Magnetron Sputter Deposition**

#### **Ming Cao 1, Lan Zhao 2, Libin Wu 3 and Wenquan Wang 1,\***


Received: 10 February 2018; Accepted: 26 March 2018; Published: 6 April 2018

**Abstract:** The increasing demands of environmental protection have led to solid lubricant coatings becoming more and more important. A new type of MoS2-based coating co-doped with Cu and Al prepared by magnetron sputtering, including Cu/MoS2 and Cu-Al/MoS2 coatings, for lubrication applications is reported. To this end, the coatings were annealed in an argon atmosphere furnace. The microstructure and the tribological properties of the coatings prior to and following annealing were analyzed using scanning electron microscopy, energy dispersive spectrometry, X-ray diffractometry (XRD) and with a multi-functional tester for material surface properties. The results demonstrated that the friction coefficient of the Cu/MoS2 coating was able to reach as low as 0.07, due to the synergistic lubrication effect of the soft metal Cu with MoS2. However, the wear resistance of the coating was not satisfied. Although the lowest friction coefficient of the Cu-Al/MoS2 coatings was 0.083, the wear resistance was enhanced, which was attributed to the improved the toughness of the coatings due to the introduction of aluminum. The XRD results revealed that the γ2-Cu9Al4 phase was formed in the specimen of Cu-Al/MoS2 coatings. The comprehensive performance of the Cu-Al/MoS2 coatings after annealing was improved in comparison to substrate heating, since the heat-treatment was beneficial for the strengthening of the solid solution of the coatings.

**Keywords:** Cu/MoS2 coatings; Cu-Al/MoS2 coatings; tribological properties; annealing treatment; γ2-Cu9Al4 phase
