Electrochemical response and passivation affinity of Fe-based amorphous HVOF coatings prepared from pig iron on mild steel

The present work discusses the passivation tendency and corrosion resistance of a novel Fe66.59C11.70P7.58Mn0.37Si2.86Cr1.72Mo0.92B8.26 amorphous coating prepared from pig-iron deposited on mild steel using a high-velocity oxy-fuel (HVOF) thermal spray process. A quantitative assessment of the micromorpho-logical features developed on each coating after the fabrication has been provided. The polarization response, current-transient at the potential in the passive zone, and gravimetric evaluations after 30 days of the salt-fog test using 3.5 w/v % NaCl solution were recorded to understand the overall corrosion behavior of the HVOF coatings. A steady-state electrochemical impedance measurement was also performed. The spectroscopic examination of the corrosion product was performed to understand the nature of passivation, and it revealed the formation of protective iron-chromate and phosphate phases on all the coatings. The synergistic effect of these protective phases and iron-based protective rust phases is believed to be the primary reason for the strong passivation of the coatings. Also, it has been proposed that the corrosion rates calculated from dynamic polarization response should not be considered as final assessment for corrosion resistance of the coatings. Rather, long term corrosion assessment is important to understand the benefit of amorphous coatings with lean chemistry of passive ele-ments, like Cr.

Automated summary

This study investigates the passivation tendency and corrosion resistance of a novel Fe66.59C11.70P7.58Mn0.37Si2.86Cr1.72Mo0.92B8.26 amorphous coating prepared from pig-iron deposited on mild steel using a high-velocity oxy-fuel (HVOF) thermal spray process. The micro-morphological features of the coatings were quantitatively evaluated. Various tests were conducted to understand the corrosion behavior, including polarization response, current-transient, gravimetric evaluations, and spectroscopic examination of the corrosion product. The results showed that the coatings had strong passivation due to the protective iron-chromate and phosphate phases.