Dislocation Substructure Gradient Formation in Aluminum by Creep under Weak Potential (original) (raw)
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Dislocation substructure evolution on Al creep under the action of the weak electric potential
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
The dislocation substructure evolution on Al creep under the action of the weak electric potential is established by methods of transmission diffraction electron microscopy. It is shown that change of the electrical potential of the Al sample surface is accompanied by the increase of dislocation substructure self-organization degree.
Journal of Applied Crystallography, 2022
In the present work, electron backscatter diffraction was used to determine the microscopic dislocation structures generated during creep (with tests interrupted at the steady state) in pure 99.8% aluminium. This material was investigated at two different stress levels, corresponding to the power-law and power-law breakdown regimes. The results show that the formation of subgrain cellular structures occurs independently of the crystallographic orientation. However, the density of these cellular structures strongly depends on the grain crystallographic orientation with respect to the tensile axis direction, with h111i grains exhibiting the highest densities at both stress levels. It is proposed that this behaviour is due to the influence of intergranular stresses, which is different in h111i and h001i grains.
Alloying effects on dislocation substructure evolution of aluminum alloys
International Journal of Plasticity, 2004
The constitutive response of aluminum alloys is controlled by the evolution of dislocation substructure including mobile and forest dislocation density, cell size distribution and morphology, and misorientation angle between neighboring cells. The present study focuses upon the small strain regime and compares the measured microstructural evolution of 3003, 5005, and 6022 aluminum alloys during deformation. Room temperature tensile deformation experiments were performed on industrially manufactured specimens of each alloy and the evolving microstructure was compared with the mechanical response. The dislocation structure evolution was characterized using transmission electron microscopy and orientation imaging of deformed specimens. It was observed that structural evolution is a function of lattice orientation and the character of neighboring grains. In general, the dislocation cell size and misorientation angle between dislocation cells evolves systematically with deformation at relatively small strain levels. #
Metallurgical and Materials Transactions A, 2002
Creep experiments were conducted on aluminum single crystals and copper polycrystals deformed within the five-power-law regime. The dislocation structure of copper, which has not been extensively characterized in the past, consists of less-well-defined subgrain walls of relatively low misorientation, typically between 0.1 and 0.3 deg, with a Frank network of dislocations within the subgrains. The aluminum, as expected, consisted of well-defined subgrain boundaries with a typical misorientation between 1.0 and 2.0 deg. The subgrains were probed from one boundary to another in copper and aluminum using convergent-beam electron diffraction (CBED). This allowed a determination of any changes in the lattice parameter, which would indicate the presence of any internal stresses. Earlier investigations by others suggested that internal stresses may be high in the vicinity of the "hard" subgrain boundaries in both loaded and unloaded specimens, based on a variety of techniques including X-ray diffraction (XRD), stress-dip tests, as well as some preliminary CBED. It was determined in this work that the lattice parameter was unchanged at the equilibrium or stress-free value within the interior of the subgrains and along (within a one-beam diameter) the subgrain boundaries.
Acta Metallurgica, 1982
The substructure behaviour of Aluminium has been studied at intermediate temperatures in order to determine the microscopic mechanisms which control the strain rate. This first article describes the detailed geometrical features of the dislocation networks after the creep test. The subboundaries are made of the dislocations emitted by the sour= which are activated by the local stress; most of them are of mixed character, exhibiting 3 coplanar Burgers vectors at 120"; their long range stress field, if any, is smaller or equal to the creep stress; the small dislocation segments are situated in their respective glide planes, which brings some restrictions on the possible network geometries. In the subsequent articles, these features will appear as essential to understand the dynamic properties of the substructure during in situ creep experiments in a high voltage electron microscope, and to work out a new picture of creep at intermediate temperatures. R&um&-Nous avons itudie le comportement de la sous-structure de dislocations pendant le fluage de I'aluminium aux temperatures moyennes, dans le but de determiner quels sont les mtcanismes microscopiques qui contr&nt la vitesse de deformation. Ce premier article d&it les prop&es gtomttriques des rtseaux de dislocations apres fluage. Lea sous-joints sont constitues par les disiocations qui se sont multipliees sous l'effet de la contrainte locale; ils sont en majorite mixtes, et composes de 3 vecteurs de Burgers coplanaires a 120"; leur champ de contrainte a longue distance. s'il existe, est infirieur ou tga) a la contrainte appliqufe; enfin, ils sont constituts de segments de dislocations situ& dans des plans de glissement ce qui impose certaines restrictions sur la gtometrie des reseaux possibles. Dans les articles suivants, ces resultats permettront de comprendre le comportement dynamique de la sous-structure. au tours d'expi$ences de fluage in situ dam un microscope tlectronique a haute tension, et d'ttablir un nouveau modele de fluage aux temperatures moyennes. zllgmmenfasatmg-Das Verhalten der Substruktur in Aluminium wurde bei mittleren Temperaturen untersucht, urn die mikroskopischen Mechanismen zu bestimmen, die die Dehngeschwindigkeit kontrollieren. Diese erste Arbeit beschreibt die einxelnen geometrischen Eigenschaften der nach dem Kriechversuch beobachteten Versetzungsnetzwerke. Die Subkorngrenxen bestehen aus Versetzungen meist gemischten Charakters, die von Quellen nach deren Aktivierung durch die lokale Spannung emittiert werden. Drei koplanare Bergersvektoren unter 120" treten auf. Das weitreichende Fcld dieser Subkomgrenzenist, wenn iiberhaupt vorhanden, kleiner oder gleich der Kriechspannung. Die kleinen Versetzungsegmente liegen in ihrer Gleitebene, welches die miiglichen Strukturen der Subkorngrenzen einschriinkt. In einer nachfolgenden Arbeit sind diese Ergebnisse wichtig fur das Verstlndnis des dynamischen Verhaltens der Substruktur wahrend der in siru-Experimente im Hochspannungseiektronensikroskop und fur die Erarbeitung eines neuen Kriechmodelles fur mittlere Temperaturen. 93 Al 99.33:: rolling by 75", Al 99.37; annealed ih at 500cC Al 99.9% annealed 1 h at 350°C Al 99.96"/, annealed 2hat3OO"C Al 99.6"/, annealed 2h at 550°C
Compact and Dissociated Dislocations in Aluminum: Implications for Deformation
Physical Review Letters, 2005
Atomistic simulations, confirmed by electron microscopy, show that dislocations in aluminum can have compact or dissociated cores. The calculated minimum stress (P) required to move an edge dislocation is approximately 20 times smaller for dissociated than for equivalent compact dislocations. This contradicts the well accepted generalized stacking fault energy paradigm that predicts similar P values for both configurations. Additionally, Frank's rule and the Schmid law are also violated because dislocation core energies become important. These results may help settle a 50-year-old puzzle regarding the magnitude of P in face-centered-cubic metals, and provide new insights into the deformation of ultra-fine-grained metals.
In-situ TEM study of dislocation patterning during deformation in single crystal aluminum
Journal of Physics: Conference Series, 2010
The evolution of dislocation patterns in single crystal aluminum was examined using transmission electron microscopy (TEM). In-situ tensile tests of single crystals were carried out in a manner that activated double slip. Cross slip of dislocations, which is prominent in all stages of work hardening, plays an important role in dislocation motion and microstructural evolution. In spite of the limitations of in-situ straining to represent bulk phenomena, due to surface effects and the thickness of the samples, it is shown that experiments on prestrained samples can represent the early stages of deformation. Transition between stage I and stage II of work hardening and evolution during stage III were observed.
Journal of Applied Crystallography, 2023
The peak broadening in neutron diffraction experiments on tensile specimens of pure Al (99.8%) and an Al-Mg alloy pre-deformed at different creep strains is analysed. These results are combined with the kernel angular misorientation of electron backscatter diffraction data from the creep-deformed microstructures. It is found that differently oriented grains possess different microstrains. These microstrains vary with creep strain in pure Al, but not in the Al-Mg alloy. It is proposed that this behaviour can explain the power-law breakdown in pure Al and the large creep strain observed in Al-Mg. The present findings further corroborate a description of the creep-induced dislocation structure as a fractal, predicated on previous work.
Dislocation mechanics of creep
Materials Science and Engineering: A, 2009
The predominance of phenomenological power laws in creep of crystalline materials indicates that the dislocation mechanics of inelastic deformation of crystalline materials has not yet been fully understood. We review the progress towards a general and comprehensive model. In general, dislocation-mediated plasticity leads to generation of dislocations in the crystal interior. Creep, i.e. plasticity at constant stress, continues only if dislocations are able to disappear again (dislocation recovery). A simple model of creep of subgrain-free materials reproduces characteristic features of steady-state creep, but shows significant quantitative deficiencies, indicating that subgrain formation must not be neglected. It is proposed that migration of low-angle subgrain boundaries constitutes the process controlling creep in most cases of single-and multi-phase materials with conventional grain size. High-angle boundaries begin to play a significant role when their spacing d approaches the steady-state subgrain size w ∞ developing in coarsegrained materials. Depending on the w ∞ /d-ratio and deformation conditions, high-angle boundaries may harden or soften the material in the steady state of deformation.