Dynamic dislocation phenomena in single crystals of Cu-10.5-at.%-Al alloys at 4.2 °K

Single crystals of Cu-10.5-at.%-Al alloys with the [{}12{}5] {1{}2{}1} {{}2{}10} orientation experience discontinuous elongations under tensile stress at 4.2 ^∘{}K. The processes are initiated at a resolved shear stress of 3.01 Kg mm^-2 on the {{}1{}11} 101> glide system. They introduce slip bands with a mean width of 47 m̄ and produce a mean integrated shear displacement of 5.7 {μ}m corresponding to the motion of 3.5 ×{} 10⁴ dislocations in near-edge orientations. Simultaneous elongation-time and stress-time records have been obtained with capacitive and ceramic piezoelectric transducers located near the site of relaxation in the cryostat. After an initial interval of 30 s̄ec, elongation proceeds at a constant rate of 1.1 cm sec^-1 for 400 {μ}sec. During this process, the shear stress is 0.024 kg mm^-2 lower than at the onset of relaxation. The rate of elongation, which is determined by the mechanical properties of the system, gives a value for the product of the number and velocity of the moving dislocations of 3.76 ×{} 10⁷ cm sec^-1. Observations of the surface topography of the slip bands and of the dislocation-etch-pit distributions within them are used to establish a model for the sequence of events during the relaxation process. With this model, the mean velocity of the dislocations is found to be 2.1 ×{} 10⁴ cm sec^-1 at a resolved shear stress of 2.98 kg mm^-2 and a local steady-state temperature of 17 ^∘{}K.