Effect of crystallisation on electrochemical properties of arc sprayed FeNiCrBSiNbW coatings

FeNiCrBSiNbW coatings were prepared using a twin wires arc spraying process and were subsequently annealed at 450, 550 and 650 degrees C for 1 h to obtain coatings with different crystallisation. The effect of crystallisation on the electrochemical properties of the coatings was investigated. Transformation of the amorphous phase to crystalline phases of alpha-(Fe, Cr), Fe3B and Fe23B6 occurred when the as sprayed coating was treated at 650 degrees C. Open circuit potential tests, potentiodynamic polarisation tests and electrochemical impendence spectroscopy were employed to investigate the corrosion resistance of the coatings in 3.5 wt-% NaCl solution. The results showed that the corrosion resistance of the coatings decreased with increasing annealing temperature, and the as sprayed coating exhibited the best corrosion resistance among the four kinds of coatings. This was attributed to the high amorphous phase content and the absence of borides such as Fe3B and Fe23B6 phases in the coating.