Ecodesign of Surface Coatings : How to Conciliate Environmental and Technical Performances ?

Hexavalent chromium was recently prohibited in the European automotive industry and electrical and electronic equipment by two directives of the European Parliament (end-of-life vehicles and RoHS). It is always accredited in the electrolytic baths of decorative chromium plating and hard chromium plating, but the regulation applying to the surface treatment industry was reinforced, in particular reclassifying the chromic anhydride among very toxic substances. The aim of our study is to improve the best available techniques (BAT) in surface coatings, relating to European IPPC directive and consequently, to research innovations in the field of dry coatings processes. To take into account the environmental aspect of these coatings from the point of view of materials and processes, life cycle assessment of the surface coatings processes was established, which constitutes a first originality of the study.

In addition, surface coatings by thermal spraying were already developed in industry. But results are not always satisfactory for reasons of porosity and microstructure. The contribution of laser cladding is also studied. It allows the construction of denser coatings. The two processes appear in fact like very complementary. Thus, it is interesting to compare the environmental and technical results obtained with these two technologies. Next, we have developed a hybrid process, which associates plasma spraying and an in situ laser treatment in order to control the microstructure of coatings to decrease their porosity and improve their mechanical and chemical properties.

Thus, the aim of this study is to propose coatings, with a justified environmental behaviour, carried out by APS, laser cladding and a post laser treatment which could replace hard chromium coatings in applications to resist against wear and/or corrosion. The originality of this step lies in the optimization of the coating processes, so as to offer alternatives, transferable properties in industrial production.