The effect of hydrogen upon the average dislocation velocities in Ni3Al single crystals was investigated (figure 30) by using the etch-pit technique. It was found that the velocity was markedly decreased by the charged high content of hydrogen and that the tension/compression asymmetry of the dislocation velocity was reversed. Detailed observation of the dislocation structure indicated that the motion of edge super-kinks was seriously inhibited by hydrogen solutes. These results serve as a strong evidence for the mechanism of hydrogen strengthening in metals. The interaction between the solute H and the edge dislocations also throws a sidelight on the role of kinks in the flow stress anomaly in Ni3Al.

A Dramatic Decrease of the Dislocation Velocity in Ni3Al Single Crystals under the Influence of Hydrogen. Jiang, C.B., Li, H., Tan, J., Wu, S.D., Rong, L.J., Patu, S.: Intermetallics, 2001, 9[4], 355-60

Figure 30

Stress dependence of dislocation velocities in

hydrogen-charged and hydrogen-free Ni3Al