Stability Of Dislocation Structures Research Articles

The Applications of Vibratory Stress Relief in High-Strength Aluminum Alloy Thick Plate

The level and distribution of residual stresses have great impact on dimensional stability, while Vibratory Stress Relief (VSR) is an effective technology to relax or homogenize residual stresses. Experimental study on residual stresses distribution, residual strain energy and machining deformation of 7075 high-strength aluminum alloy thick plate under different aging process status shows that VSR can effectively decrease the amplitude and strain energy density, and enhance stability of dislocation structures and phase states in metal microscopic volume, then internal residual stresses are homogenized to enhance components’ anti-deformation capacity. In addition, the capability in maintaining dimensional stability from VSR is better than that from traditional mechanical stretching process

Stability of dislocation structures in copper towards stress relaxation investigated by high angular resolution 3D X‐ray diffraction

AbstractA 300 µm thick tensile specimen of OFHC copper is subjected to a tensile loading sequence and deformed to a maximal strain of 3.11%. Using the novel three‐dimensional X‐ray diffraction method ‘High angular resolution 3DXRD', the evolution of the microstructure within a deeply embedded grain is characterised in‐situ by the behaviour of individual subgrains. The loading sequence consists of three continuous deformation stages with strain rates of 1.1 × 10–6 s–1 and 3 × 10–2 s–1, in each case followed by a period of extended stress relaxation at fixed motor positions, as well as an unloading step. In contrast to the deformation stages, during each stress relaxation stage, number, size and orientation of subgrains are found to be constant, while a minor amount of clean‐up of the microstructure is observed as narrowing of the radial X‐ray diffraction line profile. The associated decrease in the width of the strain distribution indicates homogenization of the elastic strains present in the deformation structure. During reloading, the subgrain structure seemingly starts to develop further when the entire dislocation structure is deforming plastically. Upon unloading of the sample, the average backward strain of the subgrains increases. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental study of the thermal stability of dislocation structures produced through cyclic deformation in copper polycrystals

Energy associated with specific dislocation configurations such as loops and dipoles has long been a topic in the field of dislocation theory. Specifically, in the past thirty years or so, discussion on the energy associated with characteristic dislocation structures such as Persistent Slip Bands (PSBs) and cell structures induced by cyclic deformation process, has attracted much more attention because the formation of such structures as PSBs is probably the most important feature of the cyclic deformation and fatigue response of high stacking fault energy materials, say Cu. The importance of such a feature, PSB formation, is reflected by the very fact that it directly indicates the most important mechanical phenomena of these materials in cyclic deformation including strain localization, formation of extrusion/intrusion pairs and, finally, fatigue crack initiation. The present study is designed and carried out in order to experimentally observe the thermal stability of dislocation structures. Specifically, as the thermal evolution of dislocation structures produced in static deformation has been discussed thoroughly by Martin et al., the author will concentrate on the evaluation of cyclic deformation-induced structures upon thermal activation. The project has been carried out in a form of comparison between cyclically deformed samples and statically deformed samplesmore » of an identical material.« less

Effect of “deformational” and thermal annealing on the stability of dislocation structure in Zn crystals

The stability of the pyramidal dislocation forest of the {11 2 2} 〈11 2 3〉 system in Zn single crystals, under repeated straining on the (0001) [2 1 1 0] slip system with intermediate annealing, has been studied. The stability of the hardened state is shown to depend greatly on the annealing temperature and the plastic deformation processes in the basic slip system. Thus, we may consider two types of annealing: deformational and thermal, whose joint influence on the crystal always has a greater effect than that of ordinary thermal annealing alone. The conclusion is drawn that the decrease of the forest dislocation density and of the yield stress are bound to a strong elastic interaction between the basal and pyramidal dislocations for forest densities above a critical value (>4 × 10 5 cm −2).