The Mechanism of Titanium Hydride Growth on Grade‑2 Titanium under Simulated Crevice Corrosion Conditions

ASTM grade-2 titanium (Ti-2) is widely used in industrial applications due to its excellent corrosion resistance. However, in these applications, crevice corrosion or galvanic coupling can cause the formation of titanium hydride (TiH _x ), potentially resulting in material failure through hydrogen-induced cracking (HIC). During the metal fabrication process, Fe impurities in Ti-2 can form Ti _x Fe intermetallic particles (IMPs) that can significantly alter the corrosion behavior of the material. This study investigates the relationship between TiH _x formation and Ti _x Fe IMPs in 0.5 M HCl at 60 °C by forming TiH _x galvanostatically for varying durations and subsequently analyzing the surface. We determined that TiH _x formation initiates at Ti _x Fe IMPs, causing swelling and creating a protrusion at these sites. Initially, the hydride grows in an arc profile around the Ti _x Fe IMP, reaching a thickness of ∼5 μm before beginning to form on the Ti matrix surface. Hydride growth into the metal occurred in preferential directions, attributed to favored H diffusion pathways. The dissolution of the Ti matrix and Ti _x Fe IMPs in the acidic solution increased with polarization time, presumably because of oxidation and/or chemical dissolution of the TiH _x formed. The potential measurements during galvanostatic polarization, XRD analysis, and electron microscopy observations all indicated that TiH _x grew rapidly over the first 4 h, followed by slower growth that increased the surface coverage.