Oxidation and hot corrosion behaviors of HVAF-sprayed conventional and nanostructured NiCrC coatings

The oxidation and hot corrosion behaviors of HVAF-sprayed conventional and nanostructured NiCrC coatings were studied. The oxidation experiment was conducted in air, and the hot corrosion was conducted in the Na2SO4-30%K2SO4 environment, in the temperature range of 550-750 °C for periods up to 160 h. The corrosion kinetics was tested with the thermogravimetric method. The corrosion products were characterized by scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD). As indicated by the results, both types of coatings possess high corrosion resistance, especially the nanostructured NiCrC coating. The enhanced grain boundary diffusion in the nanostructured coating not only promotes the formation of a denser Cr2O3 scale with a higher rate, but also helps to mitigate the Cr depletion at the metal/scale interface. The less porosity of the nanostructured coating is also thought to be beneficial to the anti-corrosion properties.