HIGH TEMPERATURE CORROSION BEHAVIOR OF SELECTED THERMALLY SPRAYED ALLOY BASED COATINGS IN AGGRESSIVE ENVIRONMENT AT 800 °C

This study is focused on the high temperature corrosion evaluation of selected thermally sprayed coatings. NiCoCrAlYHfSi, NiCoCrAlY, NiCoCrAlTaReY and CoCrAlYTaCSi coatings were sprayed on the base material 1.4923. This material is used as a cost-efficient construction material for components of power equipments. All evaluated coatings were sprayed using HP/HVOF (High Pressure / High Velocity Oxygen Fuel) technology. High temperature corrosion testing was performed in a molten salt environment typical for coal-fired boilers. All coatings were exposed to the environment of 75 % Na2SO4 and 25 % NaCl at the temperature of 800 °C under the cyclic conditions. Each cycle consisted of 1h heating in silicon carbide tube furnace followed by 20 min of cooling. The weight change measurement was performed after each cycle to establish the corrosion kinetics. Optical microscopy (OM), scanning electron microscopy (SEM) and elemental analysis (EDS) were used to analyse the corrosion mechanism. CoCrAlYTaCSi coating showed the best corrosion resistance out of all evaluated coatings, followed by NiCoCrAlTaReY and NiCoCrAlY Al the evaluated coatings performed better in this particular environment than the bare P91 a H800 steels