Mobility of Dislocations in Aluminum

Abstract

The velocities of individual dislocations of edge and mixed types in pure aluminum single crystals were determined as a function of applied-resolved shear stress and temperature. The dislocation velocities were determined from measurements of the displacements of individual dislocations produced by stress pulses of known duration. The Berg-Barrett x-ray technique was employed to observe the dislocations, and stress pulses of 15 to 108 !'sec duration were applied by propagating torsional waves along the axes of [111} oriented cylindrical crystals. Resolved shear stresses up to 16X 10 6 dynes/em• were applied at temperatures ranging from -150° to +70°C, and dislocation velocities were found to vary from 10 to 2800 em/sec over these ranges of stress and temperature. The experimental conditions were such that the dislocation velocities were not significantly influenced by impurities, dislocation curvature, dislocation-dislocation interactions, or long-range internal stress fields in the crystals. The velocity of dislocations is found to be linearly proportional to the applied-resolved shear stress, and to decrease with increasing temperature, Qualitative comparison of these results with existing theories leads to the conclusion that the mobility of individual dislocations in pure aluminum is governed by dislocation-phonon interactions. The phonon-viscosity theory of dislocation mobility can be brought into agreement with the experimental results by reasonable choices ot the values of certain constants appearing in the theory.

Acoustic emission for physical examination of metals

“…Unfortunately, their support for this model was based upon the assumption that the mean dislocation velocity did not vary during deformation from yield to fracture. This is an oversimplification; Gorman et al 62 have shown that dislocation velocity is proportional to flow stress in aluminium and it is quite possible for the mean speed of dislocations to vary by as much as a factor of 100 during a test.…”

Instabilities of High Speed Dislocations

“…For a Volterra dislocation in a linear elastic continuum, Frank [4] and Eshelby [5,6] found the elastic energy of a uniformly moving dislocation diverged at the transverse speed of sound, which suggested the existence of a limiting speed for dislocations. Early experimental studies of dislocation mobility also suggested a saturation of glide speeds as the speed of sound is approached [7][8][9][10]. Since then, continuum models of increasing complexity have been proposed to describe dislocation glide [11][12][13][14][15][16][17][18].…”

The stress-velocity relationship of twinning partial dislocations and the phonon-based physical interpretation

“…Greenman et al [24] showed experimentally that for Cu = m 0.7. For Al, Gorman et al [41] reported a linear dependence of v on at a low speed region. The measurement by Yasutake et al [25] for twinning partial dislocations in silicon suggests a distinct dependence of dislocation velocity on stress, which is better captured with = m 2.73.…”