Effect of Concentration–Time Hydrogenation Annealing Conditions on the Hydrogen Saturation of a VT23 Titanium Alloy

The kinetics of bulk and unidirectional surface hydrogen absorption by a two-phase α + β VT23 titanium alloy (Ti–Al–Mo–V–Fe–Cr) at a temperature of 800°C in the concentration range 0.2–0.8 wt % is studied. Structures from three-phase α + α" + β to single-phase β are found to form in the sample volume when the introduced hydrogen concentration is varied during bulk hydrogenation annealing. The hydrogen penetration depth and, hence, the degree of the α → β transformation are shown to be controlled by changing the hydrogenation conditions and using barrier coatings; as a result, a unidirectional gradient structure, which changes from α" + β on the side of hydrogen introduction to α + β on the opposite side, is formed. The absorption of 0.6 wt % hydrogen during unidirectional surface hydrogenation is found to proceed 20 times slower than that during bulk hydrogenation. During unidirectional surface hydrogenating, the hydrogen content in the near-surface layers is found to be 0.2 wt % higher than the introduced hydrogen concentration calculated per sample volume.