Influence of the size of spraying powders on the microstructure and corrosion resistance of Fe-based amorphous coating

The Fe-based amorphous coatings with the composition of Fe(48)Cr(15)Mo(14)C(15)B(6)Y(2) were successfully sprayed on mild steel substrate by the high velocity oxygen fuel (HVOF) spraying process with different feedstock powder sizes (i.e., powder A: -33 + 20 mu m, powder B: -45 + 33 mu m, powder C: -55 + 45 mu m). The coatings were characterized for its morphology, microstructure and thermal stability by using Xray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The corrosion behavior of the coatings in 3.5 wt% NaCl solution was studied with potentiodynamic and potentiostatic polarization test. It was found that the particle size of the feedstock powders had a significant influence on microstructure and corrosion resistance of the resultant coatings. The coatings sprayed with the finest powders show the most compact structure: while the coating with the coarser powders exhibits a better corrosion resistance. It is found that the corrosion resistance of the coatings is closely related to the wetting behavior which is affected by the oxygen content and the roughness of coatings. The coatings with hydrophobicity exhibit a better corrosion. The present result demonstrates that the amorphous coatings with hydrophobicity and excellent corrosion resistant are promising for industrial application in marine environment. (C) 2011 Elsevier Ltd. All rights reserved.