Short- and Long-Term Wettability Evolution and Corrosion Resistance of Uncoated and Polymer-Coated Laser-Textured Steel Surface

Marjetka Conradi,Aleksandra Kocijan,Tina Sever,Peter Gregorčič

doi:10.3390/coatings9090592

Marjetka Conradi, Aleksandra Kocijan + Show 2 more

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https://doi.org/10.3390/coatings9090592

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Abstract

We present the results of one year observation of wetting and corrosion properties of nanosecond fiber laser-textured stainless steel, uncoated and coated with epoxy or FAS (fluoroalkylsilane)-TiO2/epoxy. A comparative study was performed on samples kept under ambient conditions and in reduced air pressure and humidity. The results show the ability to induce wettability conversion from initially superhydrophilic to final superhydrophobic state either indirectly by ageing the uncoated laser-textured surface or directly by application of FAS-TiO2/epoxy coating. The storage conditions significantly influenced the wettability development of uncoated laser-textured steel, i.e., the process of ageing was slowed down in reduced air pressure and humidity. Detailed surface chemical analysis revealed that adsorption of the organic matters from the surrounding media influences the wettability conversion and ageing. However, the ageing of the coated surfaces was not affected by the storage conditions. Corrosion stability of uncoated laser-textured surfaces was enhanced over time due to the wettability transition, depending on their morphology. Coatings represent a superior barrier over the texture and wettability with the stable long-term surface protection against aggressive media.

Highlights

Austenitic stainless steel is known as one of the most important engineering materials due to its high corrosion resistance combined with favorable mechanical properties, such as high tensile strength [1,2]
In our previous work [19], we have shown that solely the short-term evaluation of superhydrophilic-to-hydrophobic transition after the laser texturing of metallic surface may lead to wrong conclusions
By monitoring the static water contact angles and detailed surface chemical analysis we evaluated the time-dependence of the wettability transition from a superhydrophilic to superhydrophobic state of uncoated laser-textured surfaces, as well as hydrophobic to superhydrophobic transition of coated laser-textured surfaces

Summary

Introduction

Austenitic stainless steel is known as one of the most important engineering materials due to its high corrosion resistance combined with favorable mechanical properties, such as high tensile strength [1,2]. For applications in aquatic media or in other aggressive environments, such as a chloride ion-rich environment, it is extremely important to adjust the wetting properties of the steel surface to ensure its optimal performance. This prolongs the lifetime of the material, prevents corrosion, and reduces the additional costs if the material cannot fulfil the demands of the operating conditions. To turn a surface (super)hydrophobic, the surface energy of metallic oxide surface has to be lowered.

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