Grease-free bonded coating

The new bonded coating is grease-free and also protects against corrosion / Source: Uwe Bellhäuser

Material researchers at the INM have developed a bonded coating that combines two properties. It has similar lubrication properties to those associated with greases and oils, and additionally protects against corrosion. The new material is suitable as a coating for metals and metal alloys such as steel, aluminum and magnesium.

Machine parts such as gear wheels, screw threads, cranks and bicycle chains wear if there is friction between their metal surfaces; lubricants and functional oils help prevent this. These grease-based lubricants combine with dirt, abrasion and dust, and over time form lumps or become resinous. Machine parts then have to be expensively cleaned and regreased, which means more frequent maintenance, greater consumption of resources, polluting waste and at times machine breakdowns. Researchers at the INM have now developed a bonded coating, which is grease-free and also protects against corrosion.

The thing about our bonded coating is its composition and structure, explains Carsten Becker-Willinger, Head of the Nanomers Program Division. We have incorporated platelet-like solid lubricants and platelet-like particles in a binder. When this mixture is applied to a surface, it produces a well-ordered structure in which these various particles are arranged in a roof tile pattern. This forms a so-called transfer film between the bonded coating and the object through which surfaces can slide with the minimum of friction. The particular mixture ratio means that our composite has a very low coefficient of friction. If we only used a solid lubricant, the coefficient of friction would be considerably higher.

The roof tile structure not only provides low-friction sliding, it also acts as a barrier. This is a particular advantage because as a result the material also prevents moisture or salts penetrating metal surfaces, thus also protecting against corrosion. In a neutral salt spray context, the composite has a corrosion resistance of over 1000 hours on low-alloy steel. The bonded coating can be applied using classic wet chemistry processes such as spraying or dipping. The roof tile structure forms by simple thermal curing without any further assistance in self-organization.

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