Corrosion Behavior of Fe-Based Amorphous/Nanocrystalline Composite Coating: Correlating the Influence of Porosity and Amorphicity ^†

Recently, Fe-based amorphous coatings synthesized by different thermal spraying methods have been investigated as a potential candidate for long-term surface protection of various structures due to their outstanding wear and corrosion resistance. Defects such as porosity and crystallization are inevitable in the thermal-sprayed coatings, which are introduced during the synthesis process. The corrosion behavior of these coatings is adversely affected by the presence of such defects. However, identification of a microstructural feature among amorphous content and porosity that has a greater influence on the corrosion resistance of thermal-sprayed Fe-based amorphous/nanocrystalline coating has remained elusive so far. Thus, to address this problem, in situ amorphous/nanocrystalline composite coatings were synthesized via high-velocity oxy-fuel (HVOF) spraying, along with two melt-spun ribbons of different amorphous content (one fully amorphous, FA-Rib and the other with a similar level of amorphicity to the coatings, PA-Rib). Results obtained from electrochemical characterizations, Raman analysis and Auger electron spectroscopy revealed reduced amorphicity as the primary factor that affects the corrosion behavior of such coatings. A mechanism has been proposed to explain the role of amorphicity and porosity in the corrosion behavior of Fe-based amorphous/nanocrystalline coatings. This study will ultimately help to design new amorphous composite coatings with improved corrosion resistance.