Electrochemically etched porous stainless steel for enhanced oil retention

•Electrochemically etching a 304 stainless steel makes porous, hydrophobic surface.•The porous stainless steel surface consists of hierarchical structures.•The microscale pores and bumps provide significantly enhanced oil retention.•The morphology of etched steel can be easily controlled by applied voltage.•The etched steel retains original anti-corrosion properties.

This paper reports an electrochemical etching method for stainless steel and its effect in wetting, anti-corrosion and oil retention properties. Specimens of a 304 stainless steel were electrochemically etched in diluted Aqua Regia to form hierarchically-porous surface structures, while maintaining the steel's corrosion resistance. The surfaces consist of multi-scale hierarchical structure and are highly hydrophobic, but water drops stick to it instead of rolling off because of the presence of microscale bumps. Surface structures can be controlled by changing the voltage applied during the etching process. The etched structures significantly increased the steel's oil retention because of very high roughness and steep asperity. This surface modification method could be valuable to extend the lifetime of lubrication, to improve the effectiveness of protective coatings, and to achieve oil-infused surfaces.