Cooperative phenomena at grain boundaries during superplastic flow

Zelin, M. G.; Mukherjee, Amiya K.

doi:10.1016/0956-7151(94)00428-5

Cited by 90 publications

(20 citation statements)

References 24 publications

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“…However, the formation of mesoscopic shear planes ± stretches of several coplanar grain boundaries in a row which facilitate fast deformation via sliding with little accommodation ± during the superplastic deformation of metals with grain sizes in the micrometer-region is well supported by experiments. [12] These features have also been observed in nanocrystalline materials, both by computer simulation [13] and by experiment. [6] However, more systematic investigations are required to determine how frequent these features occur and how significantly they contribute to the deformation.…”

Section: Grain Boundary Sliding and Grain Rotationmentioning

confidence: 73%

Deforming Nanocrystalline Metals: New Insights, New Puzzles

Weißmüller

Markmann

2005

Adv Eng Mater

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Recent experiments have brought new insights into the mechanisms which govern the plasticity of nanocrystalline metals. In particular, new opportunities have arisen from the finding that bulk nanocrystalline samples with extremely small grain size, prepared by the inert gas condensation technique, can be deformed to large true strain. The findings elucidate the roles of creep, partial dislocation activity along with its consequences, faulting and twinning, as well as grain boundary sliding and grain rotation. However, they also rise intriguing new questions, specifically with respect to the mechanisms of dislocation nucleation at grain boundaries, and with respect to slip system selection and alignment in twinned grains. An emerging insight is that there is not ‘the’ deformation mechanism at small grain size; instead, deformation mechanism maps in, for instance, the parameter space spanned by the strain rate and the grain size, are more appropriate representations of the various processes that control the materials behavior.

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Section: Grain Boundary Sliding and Grain Rotationmentioning

confidence: 73%

Deforming Nanocrystalline Metals: New Insights, New Puzzles

Weißmüller

Markmann

2005

Adv Eng Mater

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“…[21,22,23] However, in most regions (as marked by the letter B in Figure 7(a)), sliding occurred by grain groups, known as cooperative grainboundary sliding (CGBS), which is evidenced by lifting or heaving of a region containing several grains. [24,25] At a strain of 1.0, while the topography of the deformed specimen showed that most grains took part in GBS (Figure 7(b)), elongated groups of grains (marked by the letter C in Figure 7(b)) detected on the surface indicate that not all grains were involved in GBS as individual grains. At a strain of 1.3, nearly all grains took part in GBS, and most grains developed into striplike morphologies (Figure 7(c)).…”

Section: The Fsp Alloymentioning

confidence: 99%

Effect of friction stir processing on the kinetics of superplastic deformation in an Al-Mg-Zr alloy

Mishra

Mahoney

et al. 2005

Metall Mater Trans A

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The effect of friction stir processing on the superplastic behavior of extruded Al-4Mg-1Zr was examined at 350°C to 600°C and at initial strain rates of 1 ϫ 10 Ϫ3 to 1 s Ϫ1 . A combination of a fine grain size of 1.5 m and high-angle grain boundaries in the friction stir-processed (FSP) alloy led to considerably enhanced superplastic ductility, much-reduced flow stress, and a shift to a higher optimum strain rate and lower optimum temperature. The as-extruded alloy exhibited the highest superplastic ductility of 1015 pct at 580°C and an initial strain rate of 1 ϫ 10 Ϫ2 s Ϫ1 , whereas a maximum elongation of 1280 pct was obtained at 525°C and an initial strain rate of 1 ϫ 10 Ϫ1 s Ϫ1 for the FSP alloy. The FSP alloy exhibited enhanced superplastic deformation kinetics compared to that predicted by the constitutive relationship for superplasticity in fine-grained aluminum alloys. A possible origin for enhanced superplastic deformation kinetics in the FSP condition is proposed.

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“…The role of grain boundary sliding is often acknowledged. But whether grain boundary sliding is diffusion-accommodated [8][9][10][11], dislocation-accommodated [12,13], or a combination of both [14] remains unclear; moreover, the role of cooperative grain boundary sliding [15] or the effect of cavity formation [16] remains controversial. It seems reasonable to believe that more than one mechanism may be operating and that processing conditions and material characteristics will have a great effect on which ones are active.…”

Section: Introductionmentioning

confidence: 99%

Superplasticity in Ti–6Al–4V: Characterisation, modelling and applications

2015

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The processing regime relevant to superplasticity in the Ti-6Al-4V alloy is identified. The effect is found to be potent in the range 850-900°C at strain rates between 0.001/s and 0.0001/s. Within this regime, mechanical behaviour is characterised by steady-state grain size and negligible cavity formation; electron backscatter diffraction studies confirm a random texture, leaving grain-boundary sliding as the overarching deformation mechanism. Outside of the superplastic regime, grain size refinement involving recrystallisation and the formation of voids and cavities cause macroscopic softening; low ductility results. Stress hardening is correlated to grain growth and accumulation of dislocations. The findings are used to construct a processing map, on which the dominant deformation mechanisms are identified. Physically-based constitutive equations are presented which are faithful to the observed deformation mechanisms. Internal state variables are used to represent the evolution of grain size, dislocation density and void fraction. Material constants are determined using genetic-algorithm optimisation techniques. Finally, the deformation behaviour of this material in an industrially relevant problem is simulated: the inflation of diffusion-bonded material for the manufacture of hollow, lightweight structures.

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Cooperative phenomena at grain boundaries during superplastic flow

Cited by 90 publications

References 24 publications

Deforming Nanocrystalline Metals: New Insights, New Puzzles

Deforming Nanocrystalline Metals: New Insights, New Puzzles

Effect of friction stir processing on the kinetics of superplastic deformation in an Al-Mg-Zr alloy

Superplasticity in Ti–6Al–4V: Characterisation, modelling and applications

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