Anelastic study of screw-dislocation motion in high-purity tantalum

Abstract

The kink pair formation (KPF) process on screw dislocations in Ta was investigated by means of the anelastic creep (AEC) measurements near room temperature. The effect of σ eff on H KPF and that on ν 0 were investigated for σ eff below 16 MPa, where σ eff denotes the effective stress applied to screw dislocations responsible for the AEC through KPF, H KPF the activation enthalpy of the KPF process, and ν 0 the pre-exponential factor of the inverse of the relaxation time of the KPF process. The extrapolation of the observed σ eff dependence gives 2 H k = 0.97 ± 0.03 eV and In[ ν 0,0(s −1)] = 29.6 ± 1, where H k denotes the enthalpy of an isolated single kink and ν 0.0 is ν 0 at σ eff = 0. Both H KPF and ν 0 show a strong decrease with increasing σ eff. These features for H KPF and ν 0 are very similar to those reported for Nb and Fe after the AEC measurements. We surmise that a change in the core structure of screw dislocation plays an important role for the rate of KPF on screw dislocations in the b.c.c. metals. The AEC results are discussed together with the strong decrease in H KPF with increasing σ eff reported for Fe, Nb and Ta after the flow stress measurements.