Using macro and micro electrochemical methods to understand the corrosion behavior of stainless steel thermal spray coatings

High-velocity oxygen fuel thermal spray stainless steel coatings are desirable for their excellent erosion resistance. However, the fabrication process can lead to a decrease in corrosion resistance in comparison to the original bulk material. Here we produced stainless steel coatings on stainless steel substrates using varying deposition parameters to investigate the corrosion properties of the resulting composite steels and elucidate the corrosion behavior both on the macro and micro scale. Macro potentiodynamic polarization measurements carried out in corroding environments demonstrated the rate of degradation of the Fe-Cr alloy coating. After short immersion periods, the coatings showed iron-like active corroding behavior and no passivation regions on the anodic branch. Over time, the coating’s corrosion behavior began to change to signify similar results to that of pure chromium. Ex-situ electron microscopy and elemental composition revealed a Cr oxide rich layer left on the coating’s surface. Micro electrochemical techniques including scanning electrochemical microscopy and scanning micropipette contact method were employed over the coatings and powdered material, respectively, to show that the lack of protective passivity the thermal spray coatings possess is mostly inherited from the atomized powdered stainless steel material.