Enhancing Corrosion Resistance of Titanium Alloys\nvia Hydrothermal Etching: Nanostructure Formation under Varied Temperature\nConditions

As\na widely used material, titanium is highly sought after due\nto its significant corrosion resistance properties resulting from\nthe self-passivating natural oxide layer. Hydrothermal etching is\na promising and scalable treatment technique for synthesizing surface\nnanostructures at high and low temperatures with new mesoscopic properties.\nHowever, the corrosive behavior of hydrothermally etched titanium\nremains unknown, posing a limitation on its industrial translation.\nHere, the impact of hydrothermal conditions on the corrosive properties\nof titanium is examined for three industrially relevant titanium alloys\nat high (150 °C) and low (75 °C) synthesis temperatures.\nUsing a KOH etchant, nanotextured surfaces were fabricated on all\ntitanium surfaces, forming a mixed titania and tetra-titanate (K<sub>2</sub>Ti<sub>4</sub>O<sub>9</sub>·<i>n</i>H<sub>2</sub>O) crystal structure. Subsurface analysis revealed that the oxide\nlayer was significantly thickened (>1 μm), with total coverage\nof the bulk metal achieved for all low-temperature specimens. Electrochemical\npotentiodynamic evaluation of the nanosurfaces indicated the increased\nsurface area produced an increased corrosion current, confirming the\nsustained resistance of the fabricated nanosurface. Long-term immersion\nin fluoridated artificial saliva highlighted the increased resistance\nof hydrothermal surfaces to degradation and release of titanium, aluminum,\nand vanadium ions compared to untreated titanium alloys. The work\nprovides support for the suitability of hydrothermal nanosurfaces\nfor use in corrosive environments, a significant progression toward\nthe industrialization of the hydrothermal technique.