High-temperature corrosion behavior of selected thermally sprayed coatings in corrosive aggressive environment

The aim of this paper is to evaluate and compare the corrosion resistance of Hastelloy C-276 coating with Stellite 6 and Cr3C2% -25% NiCr coatings. The coatings were deposited using HP/HVOF (High Pressure/High Velocity Oxygen Fuel) thermal spraying technology. The corrosion test was conducted in the corrosive-aggressive environment of molten salts mixture in the composition of 40% Na2SO4-60% V2O5, simulating the corrosion environment of boilers for residual fuel oils. The corrosion test under cyclic conditions included 50 cycles at the temperature of 750 degrees C and subsequent cooling at the room temperature for 20 min. The corroded specimens were analyzed using scanning electron microscope (SEM) and elemental analysis (EDS). In comparison with Cr3C2 -25% NiCr coating, both Stellite 6 and Hastelloy C-276 coatings provided the substrate material with sufficient protection against high-temperature corrosion. The corrosion mechanism of Hastelloy C-276 coating was based on the formation of protective oxide layer which prevented further penetration of corrosive media. Stellite 6 coating exhibited the corrosion attack along splat boundaries resulting in spat delaminating into the build-up. The corrosion mechanism of Cr3C2-25% NiCr coating included the attack on NiCr matrix resulting in gradual separation of carbide phases into the corrosive environment.