HOT CORROSION MECHANISM OF NiCr - 40 % Cr3C2 HIGH-VELOCITY OXY-FUEL THERMAL SPRAY COATINGS ON STAINLESS STEEL 304

The hot corrosion characterization of High-Velocity Oxy-Fuel (HVOF) thermally sprayed coatings of 60 %NiCr[37 μm] - 40 % Cr3C2 on stainless steel 304 substrate was analysed by exposure to molten salts Na2SO4 and NaCl of various mole percentages at a temperature of 750oC. The application of finer NiCr feedstock 37 μm has been effective to improve the quality of thermal spray coatings both in physical and mechanical properties. In this study, the NiCr based coatings is evaluated in the hot corrosion test to verify its reliability. XRD and SEM characterizations were applied to analyse compounds resulting from the hot corrosion process, the depth of pitting, oxide thickness, spalling, and decarburization. Results showed that the higher the mole percentage of salt NaCl, the thicker the oxide and the deeper the pitting formed on the coating surface, and that the oxide formed was Cr2O3 and NiO. Furthermore,decarburization of Cr3C2 was severe and formed due to hot corrosion on the specimens were classified as type II, in the other hand the decarburization was not detected on the surface of the specimen after the hot corrosion test. However, spalling was evident on every specimen.