Community Research and Development Information Service - CORDIS

Environmentally safe coatings as alternatives for hard chromium

In this project existing electrodeposition systems which are practically used for corrosion and wear protection in industrial use have been evaluated and modified as well as the development of new systems to find enviromnentally safer alternatives to hard chromium.

Therefore the following coating systems were evaluated, modified or developed: Ni-W, Ni-W-P, Ni-P, Ni-Mo, Cr(III), Mn-Zn, Zn-Mn, Mn-Zn-Pb, Mn-Ti, Ti-Mn and hard nickel under direct and pulse reversed current conditions. The composition of the electrolytes and the kinetics of electrochemical deposition were studied. The resulting coatings were analyzed for morphology, microstructure, composition, wear resistance, corrosion, microhardness and roughness. Due to the interim results the final investigations were concentrated to the most prospective systems - Mn-Zn, Ni-P, Ni-P-W and Cr(III). The properties of the resulting coatings were studied and compared with hard chromium from Cr(VI) electrolytes. The results showed that Mn Zn alloy coatings - in summary - behave quite satisfactorily, followed by Ni-W-P, hard chromium from Cr(III) baths and Ni-P alloys.

To achieve these coating systems for the application in industrial practice, in a second project period the work will be concentrated to the stabilization of the electrolytes as well as to improve the economical aspects. Also industrial production tests have to be done to establish certain critical results concerning corrosive wear, corrosion, microthrowing power, wear and microstructure.

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