Thermally induced microstructure evolution and effects on the corrosion behaviors of AlFeSi metallic glass coatings

The effects of the devitrification process on the microstructure evolution and corrosion resistance of arc-sprayed AlFeSi metallic glass coatings were explored. Detailed characterizations revealed that the structural relaxation coating (annealing at 300 °C) retains the phase structures of the as-sprayed coating. Annealing at 350 °C (above the onset crystallization temperature) facilitates nanoscale Al9Fe2Si2 and Al9FeSi3 new phase precipitation. Annealing at over 400 °C (above the full crystallization temperature) induces completely crystallized structures of α-Al, Al9Fe2Si2, and Al9FeSi3 in the coatings. The crystalline size response of the coatings depends on the annealing temperatures. Electrochemical tests indicated that devitrification increases the current density and reduces the impedance of the coatings. The best corrosion resistance is discernible for the as-sprayed AlFeSi metallic glass coating. The decreased amorphous fraction, larger nanocrystals, and crystal structure heterogeneity in the as-annealed coatings are responsible for the degradation of corrosion resistance. Additionally, the variations in the compositions and natures of the passive films with thermally induced microstructure evolution were elucidated in detail. •Devitrification process significantly changes corrosion resistance of the coating.•The relationship between structure evolution and corrosion property was elucidated.•The highly stable passive film depends on Nd, EFB, We values and Al2O3 content.•The as-sprayed coating has exceptionally high corrosion resistance in Cl− solution.