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Rotational speed has an important influence on the performance of coating materials. The a-C:Ta composite coatings were prepared by controlling the substrate rotational speed during deposition process using PVD technique. The results showed that the coating transformed from dense structure to columnar structure. Due to the changes of deposition time and the vapor incident angle of the sputtering ions, the sp2 hybrid structure increased and the C–Ta bonds contents decreased as a function of the rotational speed, which led to the improvement of adhesion force. The average friction coefficient of the composite coatings did not fluctuate significantly for the amorphous carbon matrix and the transfer films formed during friction, while the wear rates were gradually increased. The sample at 0.5 rpm possessed the lowest wear rate, which was mainly associated with the cooperative behavior of the dense structure and the formation of TaC nanoclusters in the composite coating. [ABSTRACT FROM AUTHOR]

• Preparation of gallate ionic liquids (GAILs). • Their lubricating performances for copper and aluminum friction pairs are discussed. • The GAILs show prominent friction reduction and wear resistance properties. • The properties are attributed the formed physicochemical adsorbing films. In this study, four kinds of GAILs were prepared and used to lubricate copper and aluminum friction counterfaces. Their physicochemical and tribological properties were systematically investigated. The results showed that the GAILs have better performances with regard to viscosity-temperature characteristic, corrosiveness and hydrolytic stability as compared with the two traditional halogen-containing IL lubricants L-B104 and L-F104. Moreover, the most prominent nature of the GAILs are their excellent friction reduction and wear resistance properties as lubricants for copper and aluminum friction counterfaces, while traditional halogen-containing ILs are generally found to be unsuitable for lubricating these counterfaces. The excellent tribological properties of the GAILs are conjectured to be largely attributed to the physical/chemical adsorbed films formed by the GAIL molecules on the friction surfaces, which is further verified by QCM and XPS analysis results. [ABSTRACT FROM AUTHOR]