Temperature dependence of tribological properties of MoS2 and MoSe2 coatings

Transition metal dichalcogenides are well known for their lubricating properties. MoS(2) is the most popular member of this family and it is widely used as a solid lubricant in vacuum and inert gases. However, the lubricating properties of MoS(2) are deteriorated in humid air. It is known that molybdenum diselenide (MoSe(2)) has the same crystal structure and also exhibits suitable lubricating properties, but their dependence on air humidity has not been studied yet in details. This paper is aimed to the comparison of tribological properties of MoS(2) and MoSe(2) coatings measured in air of different humidity and at elevated temperatures. Both coatings were prepared by non-reactive DC magnetron sputtering and tested with ball-on-disc high temperature tribometer. The results of measurements of friction coefficient and wear rate vs. tribometer revolutions and the resulting dependencies of friction coefficient and wear rate on ambient air relative humidity are presented. These results show that the fiction coefficient of MoSe(2) was not influenced by air humidity. Wear rate of MoSe(2) in dry air was substantially higher than that of MoS(2); in humid air, the MoS(2) wear rate increased rapidly while wear rate of MoSe(2) remained unchanged. The operating temperature of both coatings was limited to 350 degrees C. (c) 2004 Elsevier B.V. All rights reserved.