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Thermo-diffusion synthesis (MoS2 based coatings)

The present result has been reached as a result of the execution of the WP3 of the Project. The main objectives of the WP3 were:
- Development of technology prototype of thermo-chemical diffusion synthesis of solid lubricant compositions based on MeS2 directly in surface layers of friction parts;
- Correlation between solid lubricant layers properties and process parameters;
- Fabrication of samples for wear tests by the developed method of thermo-chemical diffusion synthesis.

Great interest to technologies of deposition of molybdenum disulphide (MoS2) is caused by outstanding tribological properties of coatings and films. The good tribological properties of MoS2 are determined by its structure and weak bonds between S-Mo-S layers (perfect cleavage). Lubricating properties of molybdenum disulfide are especially effective in vacuum and inert gas environments over a wide range of temperature and load. Nowadays, PVD methods are successfully used in production of high-performance MoS2 coatings. However, high production cost of the methods is the strong factor limiting their wide industrial application.

The alternative method of deposition of MoS2 coatings (thermal-diffusion synthesis) is presented. This method of synthesis of MoS2 coatings comprises two stages:
(a) formation of the molybdate and molybdenum oxide layer on the surface of the steel substrate;
(b) treatment of the substrate in the vaporous sulphur environment to form MoS2.

Thickness of the MoS2 coatings varies within 5-60 microns, transition zone on the coating/substrate boundary is observed. Friction tests carried out under ambient conditions at 625-1250 MPa contact pressure showed values of the friction coefficient 0.17-0.07 respectively.

Diffusion methods of applying of synthetic molybdenum disulfide solid lubricant coatings provide the great possibilities for operational reliability of tribological assemblies operating in hostile environments (vacuum, radiation and oxygen environment, etc.) as compared with the other methods (PPS-powder plasma spraying, DPD-powder detonation deposition, PVD-physical vapour deposition, CVD-chemical vapour deposition, LCVD-laser induced chemical vapour deposition, etc.).

Current status of the results: the technology prototype was developed, the equipment prototype was designed, fabricated and installed at ENISE, numerous thermo-diffusion coatings fabricated and examined.

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Ecole Nationale d'ingenieurs de Saint-Etienne (ENISE)
58 rue J.Parot
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