Hydrogen Desorption Behavior of Pure Iron and Inconel 625 during Elastic and Plastic Deformation

The hydrogen desorption behavior of pure iron with a body-centered-cubic (BCC) lattice and Inconel 625 with a face-centered-cubic (FCC) lattice was examined during tensile deformation using a quadrupole mass spectrometer in a vacuum chamber integrated with a tensile testing machine. Hydrogen and water desorption was continuously detected simultaneously under the application of a tensile load and strain to the specimens. Hydrogen desorption promoted by tensile deformation can be found by deducting both fragment hydrogen dissociated from H2O and H2 desorbed under unloading from the total amount of hydrogen desorbed from hydrogen-charged specimens during tensile deformation. Hydrogen desorption from hydrogen-charged specimens was detected under various strain rates of 4.2×10−5/s, 4.2×10−4/s and 4.2×10−3/s. Hydrogen desorption rarely increased under elastic deformation. In contrast, it increased rapidly at the proof stress when plastic deformation began, reached its maximum, and then decreased gradually with increasing applied strain for both pure iron and Inconel 625. This desorption behavior is closely related to hydrogen dragging by moving dislocations. The amount of desorbed hydrogen promoted by tensile deformation was measured by thermal desorption analysis (TDA). The TDA results showed that the amount of desorbed hydrogen differed at each strain rate. The largest amount of desorbed hydrogen promoted by tensile deformation was 16% of the initial hydrogen content in pure iron with a high hydrogen diffusion rate when the specimen was deformed at a strain rate of 4.2×10−4/s. In contrast, that of Inconel 625 with a low hydrogen diffusion rate was 9% of the initial hydrogen content when the alloy was deformed at a strain rate of 4.2×10−6/s. This difference in the amount of desorbed hydrogen transported by dislocations depends on the balance between the hydrogen diffusion rate and mobile dislocation velocity.