**Abstract**

Bonded MoS2 film lubricants are widely used in industry as solid lubricants. It has excellent lubrication properties, but it also has characteristics that require careful consideration. As is well known, its friction and wear are greatly affected by the environmental atmosphere and its wear life depends on the pre-treatment of the substrate. It was found that in many cases the wear life could not be correctly estimated by a specific wear rate and could be explained by the fatigue life, especially under high loading conditions. The atmosphere dependent wear life can also be explained by the fatigue life.

**Keywords:** solid lubricant, coating, friction, wear, atmosphere, fatigue, space use

## **1. Introduction**

Molybdenum disulfide (MoS2), along with graphite or PTFE, is a commonly used solid lubricant. One of the most commonly used forms of MoS2 is a bonded film lubricant. Its application process is relatively simple and stable performance can be obtained, compared to other coatings such as sputtering. They are often used in automobiles and OA equipment, especially in aerospace applications.

Lubrication properties of MoS2 are known to be greatly affected by environmental atmosphere, and the same is true for bonded MoS2 film lubricants. They generally perform well in dry air, inert gas environments and in vacuum, compared to moist air environment. Because of this, they often used in space applications.

However, the performance in the atmosphere is often important even for space applications, which may be used in the atmosphere before the launching for the tests etc., and for devices that moves in and out of vacuum and the atmosphere.

The lubrication properties of bonded MoS2 film lubricant in vacuum and in air were investigated, and it was found that specific wear rate is often not effective in estimating the wear life. Fatigue at the interface between the film and the substrate is found to be the main factor that determines wear life of bonded MoS2 film lubricant, and short life in the atmosphere could be attributed to the fatigue.
