Temperature and strain-rate dependence of flow stress of tantalum in the superconducting and normal states

Flow stress changes with the transition between the superconducting and the normal states, and with the change of the strain-rate in both the states are measured as a function of temperature for high purity tantalum single crystals. The Δa−τ relation shows a significant difference between the superconducting and the normal states, while the Δa−T relation for a fixed strain-rate range does not, where Δa is the activation area, T the temperature, and τ the stress. This indicates that the softening with the superconducting transition is due to the modification of the activation enthalpy in the thermally activated motion of dislocations. The results are discussed in terms of the energy dissipation by electron scattering of the screw dislocation in overcoming the Peierls potential.