Enhancing Corrosion Resistance of Titanium Alloys via Hydrothermal Etching: Nanostructure Formation under Varied Temperature Conditions

As a widely used material, titanium is highly sought after due to its significant corrosion resistance properties resulting from the self-passivating natural oxide layer. Hydrothermal etching is a promising and scalable treatment technique for synthesizing surface nanostructures at high and low temperatures with new mesoscopic properties. However, the corrosive behavior of hydrothermally etched titanium remains unknown, posing a limitation on its industrial translation. Here, the impact of hydrothermal conditions on the corrosive properties of titanium is examined for three industrially relevant titanium alloys at high (150 °C) and low (75 °C) synthesis temperatures. Using a KOH etchant, nanotextured surfaces were fabricated on all titanium surfaces, forming a mixed titania and tetra-titanate (K2Ti4O9·nH2O) crystal structure. Subsurface analysis revealed that the oxide layer was significantly thickened (>1 μm), with total coverage of the bulk metal achieved for all low-temperature specimens. Electrochemical potentiodynamic evaluation of the nanosurfaces indicated the increased surface area produced an increased corrosion current, confirming the sustained resistance of the fabricated nanosurface. Long-term immersion in fluoridated artificial saliva highlighted the increased resistance of hydrothermal surfaces to degradation and release of titanium, aluminum, and vanadium ions compared to untreated titanium alloys. The work provides support for the suitability of hydrothermal nanosurfaces for use in corrosive environments, a significant progression toward the industrialization of the hydrothermal technique.