Distribution and thermal desorption behavior of hydrogen in titanium alloys immersed in acidic fluoride solutions

The distribution and thermal desorption behavior of hydrogen in alpha titanium (commercial pure titanium) and beta titanium alloy (Ti-11.3Mo-6.6Zr-4.3Sn) immersed in acidic fluoride solutions (pH 5.0, 25 ± 2 °C) have been investigated. For alpha titanium, most of the hydrogen absorbed in the fluoride solution existed as titanium hydride within approximately 50 μm from the surface of the specimen. The local hydrogen concentration in the vicinity of the surface was evaluated above 5000 mass ppm. Hydrogen thermal desorption was observed in the temperature range from 200 to 700 °C. It is likely that the desorption at a low temperature resulted from the dissociation of the hydride, whereas that at a high temperature was caused by hydrogen strongly trapped in matrix defects induced by hydride formation. For the beta titanium alloy, the absorbed hydrogen diffused toward the center of the specimen without hydride forming. Hydrogen was almost uniformly distributed over the whole cross-section of the specimen, although hydrogen content was high at the surface layer of the specimen. Hydrogen desorption appeared in the range from 400 to 600 °C, implying that the absorbed hydrogen was mostly hydrogen in solution. The corrosion product (TiF3) on the surface of the specimen caused the desorption temperature to rise more than 100 °C, suggesting the origin of the scatter of desorption behavior.