**4. Conclusions**

Wear life of bonded MoS2 film lubricants was found to be caused by de-bonding of the film from the substrate due to fatigue under relatively high load and low speed condition. In order to improve wear life, it is important to select substrate materials with appropriate surface morphology through pretreatment to provide

**Figure 20.** *Surface profiles of the film after the tests: (a) static loading, (b) 1 × 107 loadings, (c) 4.4 × 107 loadings [13].*

strong adhesion to the film. The specific wear rate, which assumes that the amount of wear of the material is constant according to the load and sliding distance, is not suitable for estimating the wear life of bonded MoS2 film lubricants under these conditions.

#### *Wear Life of Bonded MoS2 Film Lubricant DOI: http://dx.doi.org/10.5772/intechopen.99802*

When the thickness of the film is much smaller than the contact length, as in the case treated here, the frictional force directly becomes the shear force at the interface, which determines the fatigue life of the film-substrate adhesion. In other words, the friction coefficient has a direct effect on the wear life of the film lubricants. It was shown that the wear life of bonded MoS2 film lubricant in vacuum is much longer than in air. This is because the friction coefficient in vacuum is much smaller than in the air.

In order to improve the wear life in air, it is effective to reduce the friction coefficient in air. It is the moisture in air that increases the friction of MoS2 in air. Attempts to reduce the friction in air, such as adsorbing a surfactant on MoS2 to prevent the adsorption of water molecules and thus imparting hydrophobicity to MoS2 [15], are expected to expand the application fields of bonded MoS2 film lubricants.
