Internal friction study of dislocation mobility in deformed niobium

The γ peak associated to the thermally activated kink pair formation along screw dislocations is observed in niobium. Its relaxation characteristics are E = (0.61 ± 0.02) eV, τ∞ 10−12 s and the peak is 1.3 times wider than a single Debye peak. A systematic study of the effect of deformation amplitude and deformation temperature is made. The optimum deformation conditions to observe an important relaxation are: 160 K < Tdef < 200 K and ϵdef ≈ 5%. The γ peak anneals out in two stages: a W stage (180 to 240 K) and a × stage (280 to 350 K). These two stages are associated with a rearrangement of the screw dislocations network. This interpretation is supported by transmission electron microscopy observations.