Long-range internal stresses in cell and subgrain structures of copper during deformation at constant stress

A review of the changes of internal state related to high temperature creep of polycrystalline metals and alloys

“…shown that a group of dislocations may have a large value of internal stress when using a 5nm diameter probe size 123,127 , but a corresponding larger group using an 80nm diameter probe size may have a zero internal stress 124,125 . As a consequence the variations in the measured results from zero to a significant value could be due to an inappropriate selection of electron probe size and reflect the fact that stresses vary rapidly in the vicinity of dislocations.…”

“…As described in equation 2, the internal resistance can be derived from the measured dislocation density. In addition, the presence of high dislocation density at cell walls or sub-grain boundaries can be inferred from a detailed peak profile analysis 35,127 . Profile analysis of broadened X-ray diffraction peaks in deformed crystals was based on the theory proposed by Wilkens 142 , where both the density and arrangement of the dislocations were considered.…”

“…Jakobsen et al 130 concluded that the contribution of the sub-grain structure to diffraction peak shape cannot be described by a shifted profile broadened by a substantial dislocation density based on the soft and hard region model proposed by Mughrabi 37 . This model was used to interpret the asymmetric peak profile by X-ray diffraction 35,127 , which will be described in section 5.4.1. The observed individual sharp peak profiles, shown in Figure 12 .…”

“…A tensile internal stress of 25MPa in the sub-grain interiors was obtained for a crept specimen under compression (300°C and 162MPa). But internal stress close to the sub-grain boundaries could not be measured due to the high dislocation density in that region 127 . Straub et al 127 concluded that a 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 tensile internal stress was present in the sub-grain interiors for the specimens crept under compression.…”

“…Straub et al 127 studied Type III internal stresses induced by the presence of the dislocation cell/sub-grain structures in creep of polycrystalline Cu, using a 5nm diameter electron probe. Compression creep tests at a constant normalised applied stress, σ a /G = 4.3×10 -3 , in a temperature range from 25°C to 360°C were undertaken to generate the dislocation sub-structures.…”