Microstructures and environmental assessment of metallic NiCrBSi coatings manufactured via hybrid plasma spray process

The alternative coatings to electrodeposited hard chromium plating are studied nowadays, because of the chemical composition of the baths containing Cr(VI), forbidden by several European regulations. Thermal spraying is already used in industry, but the deposited coatings still need improvements for reasons of porosity and microstructures. In this study, atmospheric plasma spraying and in situ laser irradiation by diode laser processes were combined to modify the structural characteristics of NiCrBSi coatings. The microstructure evolution was studied, with the analysis of chemical composition using energy-dispersive spectroscopy and X-ray diffraction. Results show that in situ laser remelting induces the growth of a dendritic structure which strongly decreases the porosity of as-sprayed coatings and no phase transition after laser treatment. The adopted configuration drives to the achievement of coatings without solidification cracking, one of the major defects that can occur during the solidification of metallic alloys. Furthermore, to evaluate the environmental impacts of coatings in comparison with other conventional treatments developed to melt NiCrBSi layers, a Life Cycle Assessment was carried out. The ecodesign of surface coatings has not been reported in detail in the current literature, and nowadays, life cycle analysis is an important consideration for the thermal spray community. The good environmental assessment of the hybrid process is demonstrated in this paper.