The structure of tribologically improved MoS2–metal composite coatings and their industrial applications

Abstract

The properties of MoS2 coatings deposited by closed field unbalanced magnetron sputter ion plating have been improved by the co-deposition of small amounts of metal [D.G. Teer et al., Surf. Coat. Technol. 94–95 (1997) 572]. These initial MoS2–metal composite (MoST) coatings were hard, adherent (critical load above 120 N) low friction (μ=0.02 at 40% humidity), wear resistant and less sensitive to water vapour than pure MoS2 coatings.The MoST coating has now been further developed and improved to give a coating with higher wear resistance than that originally developed and has been tested in a variety of industrial applications, showing excellent results for a wide range of cutting and forming applications. Industrial testing of coated tools has been performed and the results are presented. Laboratory test results using microhardness testing, scratch adhesion testing, pin-on-disc and reciprocating friction and wear tests are presented. The structure of the coating has been extensively studied by a variety of techniques, including optical microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and scanning electron microscopy.The MoST coating is deposited by rotating the substrates between four targets: three MoS2 and one titanium. Because of the way in which the coating is deposited, it was initially assumed that the coating deposited could be a multilayer coating consisting of alternating layers of MoS2 and titanium. TEM and XRD analysis has been unable to detect the presence of any multilayers within the coating. Further analysis has been carried out to determine the detailed structure of the coating and the location of the titanium.TEM analysis also revealed that the MoST coating was quasi-amorphous and selected-area diffraction was unable to detect any crystalline structure. Further analysis on the amorphous nature of this coating and its stoichiometry is presented.