2009 Volume 95 Issue 7 Pages 573-581
Hydrogen desorption behaviors of pure iron with a body-centered-cubic (bcc) lattice and Inconel 625 with a face-centered-cubic (fcc) lattice were 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 hydrogen desorption out of 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 did not increase under elastic deformation. In contrast, it increased rapidly at the proof stress when plastic deformation began, and reached its maximum, then decreased gradually for both pure iron and Inconel 625. This desorption behavior is considerable related to hydrogen dragging by dislocation mobility. The desorbed hydrogen contents promoted by tensile deformation were measured using thermal desorption analysis (TDA). The TDA results showed that the desorbed hydrogen content differed at each strain rate. The largest desorbed hydrogen content promoted by tensile deformation was 16% of the initial hydrogen content in pure iron with high hydrogen diffusion rate when it was deformed at a strain rate of 4.2×10−4/s. In contrast, that of Inconel 625 with low hydrogen diffusion rate was 9% of the initial hydrogen content when it was deformed at a strain rate of 4.2×10−6/s. This deference of the desorbed hydrogen content transported by dislocations depended on the balance between the hydrogen diffusion rate and moving dislocation velocity.