Investigation of nano- and micro-scale structural evolution and resulting corrosion resistance in plasma sprayed Fe-based (Fe-Cr-B-C-P) amorphous coatings
By Kumar, Anil; Nayak, Sapan Kumar; Sarkar, Kuntal; Banerjee, Atanu; Mondal, Kallol; Laha, Tapas
Published in Surface and Coatings Technology
2020
Abstract
Fe-based (Fe63Cr9B16C7P5, at. %) amorphous/nanocrystalline coatings were synthesized by plasma spraying at various heat inputs (plasma power of 20–40 kW). Influence of heat input on the resulting microstructural evolution and subsequent effect on corrosion resistance of the coatings were investigated. Structural evolution at nano-scale studied by transmission electron microscopy revealed that degree of crystallization in the coatings increased gradually with increasing plasma power. Micro-scale distribution of amorphous and nanocrystalline phases was envisaged via contour plots of nanohardness and reduced modulus. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies demonstrated that corrosion resistance of the coatings was significantly influenced by heat input, attributed to the development of local microstructural and compositional variations. Coatings deposited at the power of 20 and 40 kW displayed higher extent of structural heterogeneities and poor corrosion resistance. However, coating synthesized at moderate power of 30 kW exhibited the best anti-corrosion behavior, i.e. the lowest corrosion current density (4.3 μA/cm2), noblest corrosion potential (−647 mVSCE) and highest charge transfer resistance (1060 Ω.cm2). The superior corrosion resistance of coating deposited at 30 kW was ascribed to the combined effect of lower porosity, higher amorphous content and formation of protective α-CrOOH and complex ferro-chromate in the coating.