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

Samantha Michelle Gateman,Alexandre Romão Costa Nascimento,Richard Chromik,Robert Lacasse,Robert Schulz,Janine Mauzeroll,Ilias Halimi,Christian Moreau

doi:10.1038/s41529-019-0087-0

Samantha Michelle Gateman, Alexandre Romão Costa Nascimento + Show 6 more

Open Access

https://doi.org/10.1038/s41529-019-0087-0

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Abstract

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.

Highlights

The success of the renewable/non renewable energy divisions, and other industrial sectors including aerospace and automotive, is significantly owed to the advancement of spray coating technologies as these coatings are essential for maintaining functionality, safety, reliability and increasing the lifetime of expensive components and machinery.[1,2] As an example, someCanadian hydropower equipment has been in service for more than 100 years because of the use of erosion mitigating technologies such as thermal spray coating methods and their ability to extend performance.[3]
SS are ferrous alloys with chromium (>12 wt%)[6] added to encourage the formation of a Cr rich oxide film over the metals surface, known as a passive film, which protects the bulk material from further degradation.[7]
This type of corrosion can be evaluated by using the bulk electrochemical technique of potentiodynamic polarization (PDP), where a sudden increase in current density during an anodic scan indicates a breakdown in the passive film

Summary

Introduction

The success of the renewable/non renewable energy divisions, and other industrial sectors including aerospace and automotive, is significantly owed to the advancement of spray coating technologies as these coatings are essential for maintaining functionality, safety, reliability and increasing the lifetime of expensive components and machinery.[1,2] As an example, someCanadian hydropower equipment has been in service for more than 100 years because of the use of erosion mitigating technologies such as thermal spray coating methods and their ability to extend performance.[3]. These results agree with the insoluble material observed after chemical digestion; where the Cr oxide shell protects some regions across the powder particle while other areas are more susceptible to corrosion due to the porosity of its exterior.

Results

Conclusion