Structual changes in copper during high-temperature creep deformation were investigated by means of the Berg-Barrett method and transmission electron microscopy.
In single crystals oriented for single slips, subgrains elongating parallel to the deformation band have been found at an early stage of transient creep. With the progress of deformation they were cut parallel to slip lines, resulting in square blocks (200∼300 μ in size), which covered almost the whole specimen surface at an early stage of steady-state creep. During steady-state creep these square subgrains were subdivided into smaller ones (50∼100 μ). Misorientation within the square subgrains and disorientation in their sub-boundaries increased very rapidly during transient creep, but remained almost constant throughout the steady-state region. On the other hand, misorientation within the smaller subgrains increased with increasing strain in the steady-state region.
In single crystals oriented for multiple slips, subdivision into small subgrains began at an early stage of creep and complex substructure eventually developed.
In polycrystalline specimens, the subgrain size subjected to creep deformation was generally small compared with single crystals. Fragmentation of a grain into a few blocks perhaps due to interactions with neighbouring grains was also observed.
In transmission electron microscopy, sub-boundaries parallel to slip plane (111) and to deformation band (110) were mainly observed, which were generally composed of more than two sets of dislocations. However, dislocation pile-ups to substantiate the X-ray finding which might suggest that substructure developes through the formation of deformation bands have never been observed.
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