Dry coatings and ecodesign part. 1 — Environmental performances and chemical properties

Abstract

Hexavalent chromium was recently prohibited in the European automotive industry, electrical and electronic equipment by two regulations of the European Parliament (End of Life Vehicles and RoHS). It is still allowed in the electrolytic baths for decorative chromium plating and hard chromium plating, but the regulation concerning the surface treatment industry was reinforced, in particular reclassifying the chromic anhydride amongst the very toxic substances. In addition, surface coatings deposited by thermal spraying have already been developed in the industry to replace the electrolytic process. But results are not always satisfactory for porosity and microstructure reasons. The contribution of laser cladding is also studied. This allows the formation of denser coatings. In fact, both processes appear to be very complementary. Thus, it is interesting to compare the environmental and technical results obtained with these two technologies. Therefore, the aim of this study is to propose coatings, with a justified environmental behaviour, carried out by thermal spray processes (APS and HVOF) and laser cladding (with a diode laser) which could replace hard chromium coatings in order to resist wear and/or corrosion. The originality of this step lies in the optimization of the coating processes, in order to offer transferable alternatives to industrial production. To take into account the environmental properties of these coatings from the point of view of materials and processes, Life Cycle Assessment of the surface coating processes was established, which constitutes the genuine characteristic of the study. The ecodesign of surface coatings has not been reported in detail in the current literature. Thus two types of materials, stainless steel and self-fluxing NiCrBSi alloy, were chosen to be the coatings on a steel substrate. Then, chemical characterization (corrosion in salt spray test) was carried out in order to determine the alternative potential of dry coatings, especially NiCrBSi coatings, compared to electrolytic hard chromium plating.