The universal topology of experimental strain–temperature maps of the dislocation structures of face-centered cubic metals permitted the ordering of dislocation structure-forming processes in these metals, which was not consistent with the stacking-fault energy or the melting temperature. Using dimensional analysis, it was shown that the metals could be ordered by the activation energy for cross slip. The experimental maps were scaled by the cross-slip activation energy to form a universal strain–temperature map. It was concluded that the transition from tangled dislocation structures to a cellular structure was related to strain–temperature conditions for spontaneous cross-slip events; associated with a constant strain of approximately 10% at low temperatures. The analysis was supported by results for single crystals of aluminium. In a system which was deformed so as to activate two slip systems it was found that, at low strains at room temperature, the dislocations were arranged into tangles, and only at strains of approximately 10% did a transition to a cellular structure with tangled walls occur. This could be explained qualitatively by recognizing that the strain required to achieve the critical stress was larger, in single crystals than in polycrystals, due to the activation of a limited number of slip systems. In contrast, the present universal map predicted that the transition from wavy dislocation walls to parallel ordering in the walls occurred at zero strain at very high temperatures. This implied that the mechanism was not based upon the cross-slip of single dislocations but perhaps upon some form of collective dynamics. It was also noted that the recovery mechanism did not scale with the dislocation activation energy; with recovery processes occurring in different metals at different scaled temperatures over the range. Thus recovery was identified as being an example of dislocation rearrangement not controlled by cross-slip.

Universal Strain–Temperature Dependence of Dislocation Structures at the Nanoscale. P.Landau, D.Mordehai, A.Venkert, G.Makov: Scripta Materialia, 2012, 66[3-4], 135-8