During plastic deformation, the transition from the normal to the superconducting state and vice versa changes the flow stress in both type-I and type-II superconductors by several percent. We have made a detailed examination of this change in flow stress by measuring its dependence on work hardening, strain rate and temperature in specimens of lead and indium. An [1 - ( T Tc)2] temperature dependence but no strain rate dependence was found. Furthermore, the shape of the stress-strain curve at the transition indicates that plastic flow actually stops when the material enters the normal state. These experimental results suggest that the dislocations are bound more securely to their pinning points in the normal state than in the superconducting state.
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