Bulk and Surface Hydrogenation Kinetics and Structure Formation in a VT22 Titanium Alloy

Abstract—The hydrogenation kinetics of a two-phase VT22 titanium alloy (Ti–5.5Al–4.3V–4.2Mo–0.8Cr–0.8Fe) is investigated depending on saturation conditions. This study demonstrates that the depth of hydrogen penetration and the completeness of the α → β transformation can be varied by controlling the concentration and time parameters of hydrogenation annealing. Furthermore, the state of the alloy can be altered from a two-phase (α + β) to a single-phase β state. Barrier coatings can be employed to regulate the direction of hydrogen penetration, thereby creating a unidirectional gradient structure. The hydrogen penetration depth of unidirectional surface hydrogenation is shown to be 1 mm greater than that of equidirectional surface hydrogenation. The rate of hydrogen absorption is found to be 1.2 times lower during surface unidirectional hydrogenation than during volumetric hydrogenation. Furthermore, the hydrogen content in the surface layer is 0.2 wt % higher than the hydrogen concentration per sample volume.