Dislocation Structures Developed during Creep Deformation of Copper Single Crystals

Abstract

Dislocation distribution and substructure formation in copper single crystals due to high temperature creep were investigated by means of the etch-pit technique and transmission electron microscopy. Etch-pit observation was made on the surfaces parallel to the primary slip plane, (111), and to the critical slip plane, (\bar111). Thin foil specimens made parallel to the primary slip plane were examined by transmission electron microscopy.
In an early stage of transient creep, subgrains elongating in the direction of the deformation band (10∼20 μ×50∼200 μ in size) have been found on the (111) plane. Cell structures (∼100 μ in size) have also been found in the region next to that of the long subgrains. With the progress of transient creep, however, the width of the long subgrains increased. At the same time, the cell structures changed into well-developed subgrain structures, decreasing in their size. In the steady-state creep region, little change was observed in the shape and the size of the substructure. The width of the long subgrains was 20∼40 μ, while the size of subgrains originating from the cell structures was ∼50 μ. This fact indicates that these two types of structures tend to become similar with the advance of creep deformation.
By the etch-pit technique, many primary dislocations were observed within the subgrains and cells in the transient creep region. The primary dislocations, which are generated during instantaneous elongation, decreased in the transient creep region and increased again in the steady-state region.
In transmission electron microscopy, random distribution of sub-boundaries of about 10 μ in length and parallel to the (\bar101)-trace was observed with a spacing of several microns perpendicular to the (\bar101)-trace, in addition to the dislocation networks lying nearly parallel to the (111) plane. The lattice distortion about the [1\bar21] axis may be ascribed to the existence of the former.