MoS2/metal composite coatings deposited by closed-field unbalanced magnetron sputtering:: tribological properties and industrial uses

In the past, MoS2, coatings deposited by sputtering have consisted of a first few layers with a dense coherent structure followed by an open columnar structure, with only the first few layers providing any wear resistance. The high ion-current densities at low substrate bias voltages, characteristic of the closed-field unbalanced magnetron sputter ion-plating system, produce MoS2, coatings that are dense: coherent and adherent with very good tribological properties. The tribological properties of these coatings have been tested by using reciprocating and pin-on-disc friction and wear machines, and the results are presented. The properties of the coatings were improved by optimising the deposition parameters, in particular by reducing the amount of water vapour present in the atmosphere of the coating system. It has been found that the properties can be further improved by the co-deposition of small amounts of metal with the MoS2. The equipment and deposition methods are described. The MoS2/metal composite coatings were harder, much more wear-resistant and also less sensitive to water vapour in the testing atmosphere. They gave excellent wear resistance at loads as high as 140 N on the reciprocating wear tester using a 6 mm diameter WC pin. The coefficient of friction was as low as 0.02 at a humidity of 40%, and the coatings and adhesion scratch tests indicated critical loads of > 120 N. The composite coatings have been studied by micro hardness testing, scratch adhesion testing, pin-on-disc and reciprocating friction and wear tests. The structure of the coatings was studied by optical microscopy and scanning electron microscopy of normal sections and taper sections produced by ball cratering techniques. Some applications, including the coating of cutting and forming tools, are described. (C) 1999 Elsevier Science S.A All rights reserved.