Relative Grain Boundary Energies in Ultrafine Grain Ni Obtained by High Pressure Torsion

Processing through the application of severe plastic deformation (SPD) has become important over the last decade because it is now recognized that it provides a simple procedure for producing fully-dense bulk metals with grain sizes lying typically in the submicrometer range. There are two major procedures for SPD processing. First, equal-channel angular pressing (ECAP) refers to the repetitive pressing of a metal bar or rod through a die where the sample is constrained within a channel bent through an abrupt angle at, or close to, 90 degrees. Second, high-pressure torsion (HPT) refers to the procedure in which the sample, generally in the form of a thin disk, is subjected to a very high pressure and concurrent torsional straining. Both of these processes are capable of producing metallic alloys with ultrafine grain sizes and with a reasonable degree of homogeneity. Furthermore, the samples produced in this way may exhibit exceptional mechanical properties including high strength at ambient temperature through the Hall-Petch relationship and a potential superplastic forming capability at elevated temperatures. This paper reviews these two procedures and gives examples of the properties of aluminum alloys after SPD processing.

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Application of Strain Gradient Plasticity Modelling to High Pressure Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.584-586.1051 ◽

2008 ◽

Vol 584-586 ◽

pp. 1051-1056 ◽

Cited By ~ 5

Author(s):

Andrey Molotnikov

Keyword(s):

High Pressure ◽

Strain Gradient ◽

High Pressure Torsion ◽

Deformation Behaviour ◽

Strain Gradient Theory ◽

Ultrafine Grain ◽

Internal Variables ◽

Gradient Theory ◽

Gradient Plasticity ◽

Dislocation Densities

An analytical model describing the deformation behaviour of copper during the high-pressure torsion (HPT) processing is presented. The model was developed on the microstructural basis where the material is partitioned in two ‘phases’, the dislocation densities in cell walls and the dislocation densities cell interior, entering the model as scalar internal variables. The resulting ’phase mixture’ model is combined with strain gradient theory to account for strain non-uniformity inherent in SPD. It was demonstrated that gradient plasticity model is capable of describing the experimentally observed trends and accounting for a homogenisation of the accumulated shear strain across the HPT sample. The predictions of the model with respect to the ultrafine grain size produced by HPT and evolution of dislocation densities are in good agreement with experimental results reported by other research groups.

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Grain boundary statistics in nano-structured iron produced by high pressure torsion

Materials Science and Engineering A ◽

10.1016/j.msea.2004.08.071 ◽

2005 ◽

Vol 390 (1-2) ◽

pp. 159-165 ◽

Cited By ~ 52

Author(s):

Yu. Ivanisenko ◽

R.Z. Valiev ◽

H.-J. Fecht

Keyword(s):

High Pressure ◽

Grain Boundary ◽

High Pressure Torsion

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Microstructural Evolution and Grain Refinement in a Cu-Zr Alloy Processed by High-Pressure Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.2635 ◽

2014 ◽

Vol 783-786 ◽

pp. 2635-2640 ◽

Cited By ~ 5

Author(s):

Jittraporn Wongsa-Ngam ◽

Terence G. Langdon

Keyword(s):

High Pressure ◽

Grain Refinement ◽

Microstructural Evolution ◽

High Pressure Torsion ◽

Electron Backscatter Diffraction ◽

Grain Morphology ◽

Grain Structure ◽

Ultrafine Grain ◽

Refinement Mechanism ◽

Ultrafine Grain Structure

A copper alloy, Cu-0.1% Zr, was processed at room temperature by high-pressure torsion (HPT) in order to evaluate the microstructural evolution and grain refinement mechanism. Transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques were employed to measure the grain morphology, grain size distributions and the distribution of the misorientation angles. The results demonstrate that this processing procedure has a potential for producing an ultrafine-grain structure containing reasonably equiaxed grain with high-angle boundary misorientations. The grain refinement mechanism is primarily governed by dislocation activities.

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Grain boundary excess volume and defect annealing of copper after high-pressure torsion

Acta Materialia ◽

10.1016/j.actamat.2013.12.036 ◽

2014 ◽

Vol 68 ◽

pp. 189-195 ◽

Cited By ~ 36

Author(s):

Bernd Oberdorfer ◽

Daria Setman ◽

Eva-Maria Steyskal ◽

Anton Hohenwarter ◽

Wolfgang Sprengel ◽

...

Keyword(s):

High Pressure ◽

Grain Boundary ◽

Excess Volume ◽

High Pressure Torsion ◽

Defect Annealing

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The State of Grain Boundaries and Grain-Boundary Diffusion in Ultrafine-Grained Mo Obtained by Severe Plastic Deformation

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.367.130 ◽

2016 ◽

Vol 367 ◽

pp. 130-139 ◽

Cited By ~ 1

Author(s):

Vladimir V. Popov ◽

A.V. Sergeev

Keyword(s):

Plastic Deformation ◽

High Pressure ◽

Grain Boundary ◽

Severe Plastic Deformation ◽

Grain Boundaries ◽

Boundary Diffusion ◽

High Pressure Torsion ◽

Grain Boundary Diffusion ◽

Fast Diffusion ◽

Non Equilibrium

The grain-boundary diffusion of Co in ultra-fine grained Mo processed by high-pressure torsion has been studied by emission Mössbauer spectroscopy and radio-tracer analysis. It is demonstrated that under the severe plastic deformation by high-pressure torsion the non-equilibrium grain boundaries are formed which are the ultra-fast diffusion paths. At annealing in the temperature range of 623-823 K the relaxation of the non-equilibrium boundaries proceeds and their properties approach to those of equilibrium boundaries of recrystallization origin.

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