Plastic Deformation of Lead in the Normal and Superconducting States

The results are given of a systematic investigation of the differences between the macroscopic characteristics of plasticity of lead single and polycrystals of 99.9992 and 99.9995% purity in the superconducting state and in the normal state at the same temperature. In the superconducting state the critical resolved shear stress of single crystals, the yield point of polycrystals, and the flow stress for different stages of deformation are lower than in the normal state. Near the fracture and at the tensile strength no difference between the flow stress in the normal and superconducting state was observed. A temperature dependence of macroscopic property changes was not found in the temperature range of 1.8 to 4.2 °K. The results obtained reveal an essential contribution from the drag due to conduction electrons to the resistance to dislocation motion. The essential interaction with conduction electrons implies that in pure metals the dislocations move with rather large velocities (102 to 105 cm/s) at low temperatures.