Evaluation of Corrosion Behavior of Plasma Sprayed Low Cr Containing Fe-based (Fe73Cr2Si11B11C3) Amorphous-Crystalline Coating

This study investigates the corrosion behavior of low-Cr and cost-effective alloying elements containing Fe-based (Fe73Cr2Si11B11C3, at.%) amorphous/crystalline coatings under 3.5 wt. % NaCl solution. Coatings were deposited using atmospheric plasma spraying (APS) at various heat inputs, corresponding to plasma power levels of 25, 30, and 35 kW, to achieve varying degrees of porosity and amorphousness. Microstructural analysis revealed that higher plasma power led to improved inter-splat bonding, but the retention of the amorphous phase decreased. This was attributed to increased powder melting and devitrification at higher plasma power levels. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) assessments indicated that the coating deposited at a moderate plasma power of 30 kW exhibited the best corrosion resistance, characterized by the lowest corrosion current density (9.7 μA/cm²), the noblest corrosion potential (−485mV), a larger semicircle diameter in the Nyquist plot, a significantly higher Bode impedance value at low frequencies and higher Bode phase angle value. The superior corrosion behavior of this coating can be attributed to the combined effects of reduced porosity, a higher amorphous content, and a lower proportion of γ-FeOOH formation.