Bulk nanostructured materials from severe plastic deformation

Massive charged particles create regions of intense damage (tracks) by passing through bulk samples of insulating materials. These tracks are shown to result from the positively charged region created by ionization. An approximate model of an ``ion explosion spike'' is proposed in which the mutual repulsion of the positive ions ejects them into the surrounding lattice. This model is shown to be generally consistent with a wide range of experimental fact. An additional damage mechanism appears to apply to polymers, in some of which tracks are produced by light projectiles such as α particles. The data here are shown to be consistent with tracks consisting primarily of broken bonds caused by decay of directly excited electrons.

Ion Explosion Spike Mechanism for Formation of Charged-Particle Tracks in Solids

The theory of the work-hardening curve of a pure single crystal is discussed. An outline is given of the experimental methods available for the study of the mechanism of plastic deformation and work hardening. An attempt is made to correlate existing theories of work hardening. The theory is illustrated by discussions of copper, of other face-centred cubic metals, of the diamond and sphalerite structures, of hexagonal close-packed metals, of ionic face-centred cubic crystals and of body-centred cubic metals.

The plasticity of pure single crystals

The density and distribution of dislocations in deformed copper crystals

Dislocation etch pit distributions and slip lines were studied on copper single crystals oriented for single glide and deformed in tension at 4·2°K. Slip lines on the cross slip plane were observed from the earliest stages of deformation and their character changed during the transition to stage II. The distribution of forest dislocations is much more isotropic and less homogeneous than that of dislocations crossing other planes. The ratio of the forest to other dislocation densities in stage I is about 1:15 but tends to 1 in stage II. The flow stress correlates better with the forest than with main glide dislocation density; twist experiments support this conclusion.

Dislocation distributions in deformed copper single crystals

A modification of an etch discovered by Lovell and Wernick has been shown to be a reliable means of revealing dislocations as etch pits on (111) faces of copper crystals. The etch has been employed to study dislocation distributions in as‐grown, annealed, and deformed crystals.A high‐temperature anneal is found to lower the dislocation density of melt‐grown crystals. A ``double‐etch'' technique is employed to observe the motion of dislocations, and to show that the dislocations initially present in these crystals are mobile at low stresses. Subboundaries are numerous in these crystals and are found capable of hindering dislocation movement. Observations of the dislocation structure of crystals deformed in bending and in tension are reported, including the appearance of ``glide polygonization'' after room‐temperature deformation.

J. D. Livingston

Papers

Etch Pits at Dislocations in Copper