Superplastic behavior of Zn–22%Al containing nano-scale dispersion particles

Xun, Yuwei; Mohamed, Farghalli A.

doi:10.1016/j.actamat.2004.03.039

Cited by 47 publications

(35 citation statements)

References 32 publications

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“…Equally important are the substructural features observed in the alloy [19] following deformation. These features are typical of those reported for micrograin superplasticity in Zn-22 % Al that contained dispersion particles (introduced via cryomilling) [9,10]. First, an equiaxed grain structure was present after extensive creep deformation.…”

Section: Superplasticity In Ultrafine-grained Materialssupporting

confidence: 54%

“…These particles were introduced in the matrix of the alloy via powder metallurgy followed by cryomilling [11]. TEM examination of specimens deformed at a strain rate near the center of the superplastic region have revealed the following observations [9,10]: (a) the initial microstructure is nearly dislocation free, (a) after deformation, only some grains contain dislocations, which interact with dispersion particles, (c) the configurations of the lattice dislocations in the interiors of these grains are suggestive of viscous glide and single slip, and (d) most of the dislocations are parallel; they tend to be long and curved; and they appear to sweep across the grain interior one by one. Fig.…”

Section: Superplasticity In Micrograined Materialsmentioning

confidence: 99%

“…Two detailed investigations in which the technique of transmission electron microscopy (TEM) wasused were carried out [9,10] in an effort to examine whether lattice dislocations were active during superplastic flow. In these two investigations [9,10], experiments were conducted on the superplastic Zn-22%Al eutectoid containing nanometer-scale dispersion particles. These particles were introduced in the matrix of the alloy via powder metallurgy followed by cryomilling [11].…”

Section: Superplasticity In Micrograined Materialsmentioning

confidence: 99%

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Effect of grain refinement on superplasticity in micrograined materials

Mohamed¹

2015

LoM

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Under superplasticity conditions, micrograined materials (grain sizes in the range 1 µm -10 µm) exhibit extensive neck-free elongations during tensile deformation at elevated temperatures (T>0.5T m , where T m is the melting point). The deformation mechanism responsible for such behavior is based on grain boundary sliding accommodated by the generation and movement of lattice dislocations in the grains blocking sliding. Such a mechanism is characterized by a stress exponent of 2, an activation energy that is close to that for boundary diffusion, and a grain size sensitivity of 2. When the grain size of the material is refined to the ultrafine-grained range (300 nm-900 nm), there is no change either in the characteristics of superplasticity or in the details of its deformation mechanism. By contrast, when the grain size of the material is refined to the nanoscale range (grain size ≤100 nm), superplasticity is lost due to the emergence of a new deformation mechanism. This new deformation mechanism is also based on grain boundary sliding accommodated by lattice dislocations. It is characterized by a stress exponent that is high and variable, an activation energy that is close to the activation energy for boundary diffusion but decreases with increasing applied stress, and a grain size sensitivity of 3.Keywords: boundary sliding, deformation mechanisms, nanocrystalline materials, ultrafine grained materials Влияние измельчения зерен на сверхпластичность в мелкозернистых материалах В условиях сверхпластичности мелкозернистые материалы (размер зерен в интервале 1-10 мкм) демонстрируют большие удлинения без шейки при деформации растяжением при высоких температурах (T>0.5T m , где T m -тем-пература плавления). Механизм деформации, ответственный за такое поведение, основан на зернограничном про-скальзывании, аккомодируемом генерацией и движением решеточных дислокаций в зернах, блокирующих про-скальзывание. Этот механизм характеризуется показателем напряжения 2, активационной энергией, которая близка к активационной энергии диффузии по границам, и чувствительностью к размеру зерен 2. Когда размер зерен ма-териала измельчается до интервала, соответствующего ультрамелкозернистым материалам (300-900 нм), ни в ха-рактеристиках сверхпластичности, ни в деталях деформационных механизмов не происходит никаких изменений. Однако когда зерна измельчаются до наноразмерного уровня (размер зерен менее 100 нм), сверхпластичность теря-ется из-за появления нового деформационного механизма. Этот новый деформационный механизм также основан на зернограничном проскальзывании, аккомодируемом решеточными дислокациями. Он характеризуется показате-лем напряжения, который имеет высокое изменяющееся значение, активационную энергию, которая близка к акти-вационной энергии диффузии по границам, но уменьшается с увеличением приложенного напряжения, и чувстви-тельностью к размеру зерен 3.

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Section: Superplasticity In Ultrafine-grained Materialssupporting

confidence: 54%

Section: Superplasticity In Micrograined Materialsmentioning

confidence: 99%

Section: Superplasticity In Micrograined Materialsmentioning

confidence: 99%

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Effect of grain refinement on superplasticity in micrograined materials

Mohamed¹

2015

LoM

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“…Classical example of a superplastic material is the Zn-Al eutectoid alloy (Zn-22Al) [1,2]. The maximum strain attainable during tensile deformation of this alloy depends critically on the strain rate, testing temperature, and the initial grain size [1][2][3][4][5][6][7][8][9][10]. Strains up to 3,000 % have been observed in a region where the relationship between flow stress and strain rate exhibits a maximum slope (region II) [1][2][3][4][5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 98%

Superplastic behavior of Zn–Al eutectoid alloy with 2 % Cu

2012

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The effects of deformation temperature and strain rate on the superplastic behavior of the Zn-21Al-2Cu alloy (Zinalco alloy) were investigated by uniaxial tensile tests. Results were compared with those of the Zn22Al eutectoid alloy without Cu. It was observed that additions of 2 % Cu leads to a decrease of the maximum strain attainable from 2600 % to 1000 %. The maximum strain in Zinalco alloy is obtained at lower strain rates. The presence of Cu increases the values of flow stress up to 600 % compared with those reported in the Zn-22Al alloy. Grain size sensitivity (p), true activation energy (Q t ), and constant A of the constitutive equation were not affected by presence of Cu unlike the stress exponent (n) which increased from 2.5 to 3.9. The main effect of Cu was to decrease the plastic flow stability of the Zn-22Al alloy.The results indicate that presence of Cu in the Zinalco alloy causes a hardening effect at low strain rates leading to a decrease in the strain rate sensitivity which promotes the formation and growth of sharp necks. Microstructural characterization suggests that the large deformations at necking could possibly be due to the substantial elongation capability of the Zn-rich phase (g).

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“…In this context, it was reported that the microstructure of the superplastic MG Zn-22 pct Al alloy after deformation contained very limited isolated dislocations but that when nanoscale particles were very recently introduced in the alloy, an extensive level of dislocation activity was noted in some of the grains. [52,53] …”

Section: Discussionmentioning

confidence: 99%

Deformation Mechanisms in Nanocrystalline Materials

Mohamed

Yang

2009

Metall Mater Trans A

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As a result of recent investigations on nanocrystalline (nc) materials, extensive experimental data on the deformation behavior of these materials have become available. In this article, an analysis of these data was performed to identify the requirements that a viable deformation mechanism should meet in terms of accounting for the mechanical characteristics and trends that are revealed by the data. The results of the analysis show that a viable deformation mechanism is required to account for the following: (1) an activation volume the value of which is in the range 10 to 40 b 3 ; (2) an activation energy that is close to the activation energy for boundary diffusion but that decreases with increasing applied stress; (3) the magnitudes of deformation rates that cover wide ranges of temperatures, stresses, and grain sizes; (4) inverse Hall-Petch behavior; and (5) limited ductility. The validity of available deformation mechanisms for nc materials is closely examined in the light of these requirements.

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Superplastic behavior of Zn–22%Al containing nano-scale dispersion particles

Cited by 47 publications

References 32 publications

Effect of grain refinement on superplasticity in micrograined materials

Effect of grain refinement on superplasticity in micrograined materials

Superplastic behavior of Zn–Al eutectoid alloy with 2 % Cu

Deformation Mechanisms in Nanocrystalline Materials

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