Caratterizzazione microstrutturale ed elettrochimica di rivestimenti per applicazioni in campo energetico

Research and development is very important in energy field as far as the available technologies are too expensive and show some problems regarding the corrosion resistance. The exploited energy reservoirs contain an high amount of aggressive chemical species, for this reason the mechanical components, employed in power plants, require high mechanical strength, thermal stability and high resistance to aggressive environments. The aim of this work was the comparison of different coatings, possible candidates for energy field applications, by means of microstructure and corrosion resistance. These coatings were deposited on ASTM 387 grade 22 steel, an alloy with high creep strength but low corrosion resistance. The selected coatings were deposited with three different technologies: 2 thermal spray processes and Ni-P electroless deposition. In particular the steel substrate was coated with: Ni-P coatings obtained by electroless process, cermet or metal alloy coatings sprayed with HVOF technology and ceramic coatings sprayed with APS technology. The tested coated systems configuration were: substrate+coating, substrate+interlayer+coating and some of this systems were also treated with epossidic resin to seal the porosity and increase the corrosion resistance of the coated steel. The various samples were morphologically characterized with optical microscope, determining the coating thickness and the porosity; the microstructure and chemical composition was verified with SEM EDXS and the average micro hardness was acquired. The corrosion resistance was evaluated by polarization curves. These curves were acquired using a potentiostat with a three electrode configuration in sulphide and chloride containing media. The solution composition simulate an aggressive environment, similar to petrochemical or geothermical one.