Effect of porosity defects on the long-term corrosion behaviour of Fe-based amorphous alloy coated mild steel

•Long-term corrosion behaviour of Fe-based amorphous alloy coated steel was studied.•The correlation between porosity defects and corrosion resistance was investigated.•The components of the surface films formed on coating surface were inhomogeneous.•Direct evidence of Cr-depleted zones around porosity defects was confirmed.

The correlation between the porosity defects, inevitably existed in thermally sprayed Fe-based amorphous coating, and the long-term corrosion behaviour of the coated steels have been studied by salt spray tests, electrochemical measurements, XPS and ToF-SIMS techniques. It has been found that porosity defects reduce the long-term corrosion resistance, increase the passive current density and lower the stability of the passive film. The deteriorated corrosion resistance is ascribed to the reduced Cr:Fe atom ratio around the porosity defects that is demonstrated by ToF- SIMS. These results provide a guide for the design of corrosion-resistant amorphous alloy coatings for engineering applications.

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