Effects of the hydrogen absorption conditions on the hydrogen embrittlement behavior of Ni-Ti superelastic alloy

The present study has investigated whether the hydrogen embrittlement behavior of Ni-Ti superelastic alloy can be changed by modifying the hydrogen absorption conditions. Upon immersion in H ₂SO ₄ or H ₃PO ₄ solution, the stress plateau due to the stress-induced martensite transformation becomes unclear and forms a gentle slope. In addition, the superelastic strain decreases with increasing immersion time. The peripheral part of the fracture surface of the immersed specimens is flat as usual, whereas the center part of the fracture surface is rough compared with that under other hydrogen absorption conditions reported previously. For the specimens immersed in H ₃PO ₄ solution, hydrogen thermal desorption tends to be observed at higher temperatures compared with the specimens immersed in H ₂SO ₄ solution. Moreover, for a longer immersion time, a second peak of hydrogen desorption is observed at a high temperature, indicating that the hydrogen states change with the hydrogen absorption conditions. The results of this study suggest that changing the hydrogen embrittlement behavior by modifying the hydrogen absorption conditions may enable the determination of the embrittlement mechanism of the alloy. ent.