Hot Corrosion Behavior of Selected Thermally Sprayed Alloy Based Coatings

Abstract

Abstract Corrosion resistance of coatings deposited by thermal spraying technology HVOF (High Velocity Oxygen Fuel) requires high density in coating and good adhesion to substrate material. The majority of thermally sprayed materials meet the requirements of high corrosion resistance in terms of their composition. However, porous structure raises doubts about the performance of thermally sprayed coatings regarding sufficient protection to the base material. In fact, corrosion protection is a basic coating function. However, , no sufficient attention has been dedicated to the issue of component protection against corrosion attack using HVOF sprayed coatings. In this study, NiCoCrAlY, NiCoCrAlTaReY, NiCoCrAlYHfSi, and CoCrAlYTaCSi coatings were deposited on the substrate material 1.4923. The coatings were deposited using HP/HVOF (High Pressure / High Velocity Oxygen Fuel) thermal spraying technology. The coatings were exposed to the corrosive-aggressive environment in the form of molten salts mixture with composition of 60 % V2O5 and 40 % Na2SO4 at the selected temperature of 750 °C. Further, all coatings were exposed to cyclic conditions. Weight changes of individual specimens were measured after every cycle and results were recorded in diagrams. After the corrosion test, all evaluated coatings were analyzed using scanning electron microscope (SEM), analysis of elemental composition (EDS) and X-Ray diffraction. The NiCoCrAlY and NiCoCrAlTaReY coatings showed the best corrosion protection in selected corrosive aggressive environment, forming the protective oxide layer that prevented further corrosion attack. On the contrary, NiCoCrAlYHfSi and CoCrAlYTaCSi coatings were found not to be suitable for corrosion protection of components working in selected corrosive environment.