Study on Solid Lubricant Films adapted for Both Environment of Vacuum and Air Atmosphere by Prevention of Galvanic Corrosion and Strengthening of Bonding Layer

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Molybdenum disulfide films with various densities have been prepared on SUS440C steel substrate by radio frequency sputter deposition. Films were stored in air atmospheres of 30% relative humidity. The effects of storage period on the wear life in air atmospheres of 9% relative humidity have been investigated using newly developed testing device. The variety in the wear life was divided into two patterns for density. The wear life of films with the density under 3.7g/cm^3 decreases with the storage period. As the density was smaller, the storage period until the wear life began to drop became shorter. On the other hand, for the film with a density of 4.3g/cm^3, the wear life increases and then decreases by the storage in air. It was found by the SIMS analysis that the oxygen in the film near film/substrate interface increases as the storage period extends.It was also found that the relationship between the wear life and film thickness depends on the crystalline orientation of sputtered molybdenum disulfide. In the case for the films with the density over 3.7g/cm^3, the wear life is scarcely influenced by the film thickness since the detachment of the film occurs readily ; the C axis of molybdenum disulfide crystal is fast oriented perpendicular or oblique direction to the substrate surface. On the other hand, for the film with a density under 2.7g/cm^3, the wear life increases with the film thickness ; the C axis is weakly oriented perpendicular or oblique direction to the substrate surface. That is, the adhesion strength of the film is strongly related to the crystalline orientation of sputtered molybdenum disulfide.On the basis of the results mentioned above, new film structure to endure the storage in air atmospheres and having a longer wear life was proposed.