Geometrical aspects of superplastic flow

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

doi:10.1016/0921-5093(95)10080-6

Cited by 83 publications

(22 citation statements)

References 36 publications

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“…The spherulitic domains initially present in some samples progressively disappear within increasing strain but slightly disturb the regular spacing of porosity bands at lower strain. The formation of a shape-preferred orientation at constant grain shape in combination with the occurrence of cavities suggests cooperative grain boundary sliding [Zelin and Mukherjee, 1996]. In our experiments, the shear bands show an orientation and kinematics that are similar to those of C′-type or ECC (extensional crenulation cleavage) shear bands from natural mylonite zones [Passchier and Trouw, 1996].…”

Section: Microstructuresupporting

confidence: 60%

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Rybacki¹,

Wirth²,

Dresen³

2010

J. Geophys. Res.

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[1] We performed high-strain torsion experiments on fine-grained (≈4 mm) anorthite aggregates in a Paterson-type gas deformation apparatus. The dense hydrous (≈0.1 wt% H 2 O) samples contain < 3 vol% Si-enriched residual glass located at triple junctions. Specimens were twisted at constant rate to a maximum shear strain of about 5 at experimental conditions of 100-400 MPa confining pressure, temperatures of 950°C-1200°C, and shear strain rates of ≈2 × 10 −5 , 5 × 10 −5 , and 2 × 10 −4 s −1 . Resulting maximum shear stresses at the sample periphery were in the range of ≈2-80 MPa. The samples showed strain hardening at slow deformation rate and strain weakening at fast strain rate, respectively. Fitting the stress strain rate data to a power law yields linear viscous behavior. Microstructural analysis shows locally enhanced dislocation density, suggesting diffusion-assisted and/or dislocation-assisted grain boundary sliding as the dominant deformation mechanism. Deformed samples exhibit abundant cavities, nucleated mostly at grain triple junctions and at grain boundaries in response to cooperative grain boundary sliding. At shear strains ≥ 2, growth and coalescence of the cavities form an anastomozing network of regularly spaced strings oriented at about 30°to the direction of maximum compressive stress and ∼15°to the shear plane. Strain is localized along these shear bands associated with a shape-preferred orientation of high-aspect ratio feldspar grains and with segregation of initial pore fluids (residual glass) into the bands. More than one third of the samples were deformed to terminal failure that occurred suddenly at shear strains of ≈3-5. The experiments indicate that cavitation damage may facilitate fluid flow and deep seismicity in highly strained shear zones.Citation: Rybacki, E., R. Wirth, and G. Dresen (2010), Superplasticity and ductile fracture of synthetic feldspar deformed to large strain,

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Section: Microstructuresupporting

confidence: 60%

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Rybacki¹,

Wirth²,

Dresen³

2010

J. Geophys. Res.

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“…Thus, as in the case of Pb-Sn eutectic alloy, the appearance of region I was attributed to the presence of impurities and their influence on GBM and dislocation motion, which were needed for the accommodation of GBS. The dominance of GBS was considered in developing several models for superplastic deformation 1,5,34 but the variation in their approaches was in terms of the details of the accommodation processes. Experimental observations and theoretical considerations suggests that GBS takes place either at individual grain boundaries or along the common surface of many grains (cooperative GBS).…”

Section: Grain Boundary Slidingmentioning

confidence: 99%

Interfacial phenomena and microstructural evolution during superplastic deformation

Kashyap

2001

Surface & Interface Analysis

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Certain polycrystalline materials of fine equiaxed grains of size <10 µm exhibit tensile ductility of several hundred to a few thousand per cent, called superplasticity, at intermediate strain rates and high temperatures. Experimental and theoretical results on mechanisms for superplastic deformation and concurrent microstructural evolution are reviewed to understand the role of grain boundary phenomena towards enhancement of grain growth and cavitation, etc. Grain boundary sliding (GBS) dominates superplastic flow, the extent of which varies between the grain and interphase boundaries in twophase alloys. Accommodation to GBS is provided by diffusional and dislocation mechanisms, which are manifested in the form of grain boundary migration (GBM), grain rotation and grain switching events. Although GBS helps in retaining the initial equiaxed grain shape of superplastic materials, the accommodation processes accelerate grain growth. In the lack of other accommodation processes the cavities are formed, being more pronounced at the boundaries of maximum sliding. The ppm-level impurities present in superplastic materials do not influence the sliding and flow characteristics under typical superplastic conditions but they do promote cavitation and limit the ductility. The presence of precipitate or hard particles in quasi-single-phase superplastic materials inhibits GBM but provides sites for cavitation. Such materials exhibit more dislocation activities than anticipated for accommodation of GBS. The nature of microstructural changes noted during superplastic deformation supports the operation of cooperative GBS, in addition to a large variety of combinations between sliding and accommodation processes.

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“…The rheological similarity between fine-grained ice and superplastically deformed metals and ceramics led Goldsby and Kohlstedt [1997] to identify the mechanism in their samples as grain boundary sliding (GBS), which embodies numerous microstructural styles [e.g., Zelin and Mukherjee, 1995] that have the common feature that grain boundaries are very mobile.…”

Section: Grain-size-sensitive (Gss) Creepmentioning

confidence: 99%