Dislocation breakaway at low temperatures in Nb

Dislocation motion at low temperatures in high purity Nb is studied by using dislocation breakaway phenomena. A strain amplitude dependence at constant temperatures or a temperature dependence at constant strain amplitude of the internal friction and the resonant period of vibration of about 600 Hz is measured to detect dislocation breakaway. Three stages of dislocation breakaway probably from hydrogen pinners can be detected below liquid nitrogen temperature. Activation parameters obtained from the breakaway measurements suggest that they correspond with the three types of dislocation motion: the kink diffusion along non-screw dislocations takes place at the lowest temperatures which is followed by the kink diffusion along screw dislocations, then the kink pair formation on non-screw dislocations takes place. After these breakaways, two relaxation peaks (the α1- and α2-peaks) emerge in the internal friction which are considered to be caused by the last two types of dislocation motion. (author)