Microstructure and properties of FeCrNiMoCBSi amorphous / nanocrystalline composite coatings via plasma spraying process

Fe-based amorphous coating technology is recognized as an attractive surface modification method owing to superior physical and chemical properties. Novel FeCrNiMoCBSi coatings were prepared on marine F22 steels by plasma spraying with various spraying powers. Morphologies and microstructures were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD), transmission electron microscope (TEM) and differential scanning calorimetry (DSC). Results showed that the as-sprayed coatings were mainly composed of amorphous and nanocrystalline phases. Spraying power had an effect on the combination of the phase compositions and defects in the as-sprayed coatings. Besides, the increase in spraying power accelerated the melting of feedstock materials, and reduced the unmelted particles existed in the coatings, but aggravated oxidization of melted particles. Spraying power affected the cooling rate, which was related to the heat input and pre-deposited surface temperature. The optimized spraying power was 35 kW, and the coating possessed an amorphous phase content of 67.8% and a defect ratio of 0.99%. Furthermore, the nanoindentation measurements showed that amorphous phase determined performance characteristics while the defects in coatings provoked local imbalances in mechanical properties. Besides, the electrochemical corrosion methods indicated that the coating sprayed at 35 kW displayed better corrosion resistance in marine environment, which was attributed to the optimized microstructure. This research not only extends the application of Fe-based amorphous coatings on marine steels, but also provides a brief sight on the relationship between processing, microstructures and properties.