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

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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Effect of Post-annealing on Grain Boundary of Nano-crystalline Cu Processed by Powder High-Pressure Torsion

Metallurgical and Materials Transactions A ◽

10.1007/s11661-014-2466-z ◽

2014 ◽

Vol 45 (11) ◽

pp. 4748-4752 ◽

Cited By ~ 3

Author(s):

Eun Yoo Yoon ◽

Dong Jun Lee ◽

Lee Ju Park ◽

Sunghak Lee ◽

Mohamed Ibrahim Abd El Aal ◽

...

Keyword(s):

High Pressure ◽

Grain Boundary ◽

High Pressure Torsion ◽

Post Annealing ◽

Nano Crystalline

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Grain Boundary Structure and Deformation Defects in Nanostructured Al–Mg Alloys Processed by High Pressure Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.584-586.528 ◽

2008 ◽

Vol 584-586 ◽

pp. 528-534 ◽

Cited By ~ 6

Author(s):

M. Liu ◽

Hans Jørgen Roven ◽

Tamás Ungár ◽

L. Balogh ◽

Maxim Yu. Murashkin ◽

...

Keyword(s):

High Pressure ◽

Grain Boundary ◽

Line Profile ◽

High Pressure Torsion ◽

Boundary Structure ◽

X Ray ◽

Grain Boundary Structure ◽

Average Grain Size ◽

Deformation Defects ◽

Non Equilibrium

An Al–0.5 Mg alloy and a commercial AA5182 alloy were subjected to high pressure torsion (HPT) to five turns under pressure of 6 GPa at room temperature. The grain boundary structure and deformation defects were investigated after HPT using high-resolution transmission electron microscopy (HRTEM). Low-angle, high-angle, equilibrium and non-equilibrium grain/subgrain boundaries, twin boundaries, full dislocations, dipoles, microtwins and stacking faults were identified by HRTEM. Extrinsic 60° dislocations in the form of dipoles were frequently observed in non-equilibrium grain/subgrain boundaries. In addition subgrain size distributions and dislocation densities were quantified by x-ray line profile analysis. It was observed that the average grain size decreased from about 120 nm to 55 nm as the Mg content increased from 0.5 to 4.1 wt%. Concomitantly the average stored dislocation density increased from 1.7 to 12.8  1014 m-2. Based on the HRTEM investigations and the x-ray line profile analyses, the deformation mechanism associated with the typical grain boundaries and deformation defects in the aluminium alloys were discussed.

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Overview of the Grain Size Effects on the Mechanical and Deformation Behaviour of Electrodeposited Nanocrystalline Nickel − From Nanoindentation to High Pressure Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.633-634.85 ◽

2009 ◽

Vol 633-634 ◽

pp. 85-98 ◽

Cited By ~ 3

Author(s):

B. Yang ◽

Horst Vehoff ◽

Reinhard Pippan

Keyword(s):

Grain Size ◽

High Pressure ◽

Grain Boundary ◽

Strain Rate ◽

High Pressure Torsion ◽

Deformation Mechanisms ◽

Nanocrystalline Nickel ◽

Deformation Processes ◽

Rate Controlled

A summary of experimental results from nanoindentation, strain rate-controlled tension, in-situ bending and high pressure torsion on bulk electrodeposited nanocrystalline nickel, focusing on the effects of grain size on the mechanical behaviour and deformation mechanisms is presented. The interaction between dislocations and grain boundaries was locally examined by studying the dependence of nanohardness on grain size and indentation size; this is done by always performing nanoindents in the center of individual grains and by varying the grain size and indentation depth systematically. The grain size effects on the different deformation mechanisms of nanocrystalline nickel were revealed by strain rate-controlled tension and nanoindentation experiments, which show that with decreasing grain size the strain rate sensitivity increases and the activation volume decreases, indicating increased grain boundary mediated deformation processes in nanocrystalline nickel. Creep experiments at room temperature revealed that in nanocrystalline nickel grain boundary sliding or diffusion along the interface may dominate at lower stress levels, but with increasing stresses the deformation process is mainly controlled by dislocation creep. In-situ bending experiments in an atomic force microscope revealed directly that grain boundary mediated deformation processes play a significant role in nanocrystalline nickel, which is also supported by the observation of grain coarsening and softening of nanocrystalline nickel caused by high pressure torsion.

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Emission Nuclear Gamma-Resonance Spectroscopy of Grain Boundaries in Coarse-Grained and Ultrafine-Grained Polycrystalline Mo

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.364.147 ◽

2015 ◽

Vol 364 ◽

pp. 147-156 ◽

Cited By ~ 4

Author(s):

Vladimir V. Popov ◽

A.V. Sergeev ◽

A.V. Stolbovsky

Keyword(s):

High Pressure ◽

Grain Boundary ◽

Grain Boundaries ◽

High Pressure Torsion ◽

Boundary Segregation ◽

Grain Boundary Segregation ◽

Coarse Grained ◽

Resonance Spectroscopy ◽

Nuclear Gamma Resonance ◽

Ultrafine Grained

Grain boundaries in coarse-grained Mo with grain boundaries of recrystallization origin and in ultrafine-grained (UFG) Mo obtained by high pressure torsion have been studied by the emission Mössbauer spectroscopy on the57Co (57Fe) nuclei. It is demonstrated that Co atoms diffuse along grain boundaries by interstitials. The temperature dependence of grain-boundary segregation factor of Co in coarse-grained Mo has been determined. It is shown that the state of Co atoms in grain boundaries and near-boundary areas in UFG Mo differs from that in coarse-grained Mo.

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Using High-Pressure Torsion to Achieve Superplasticity in an AZ91 Magnesium Alloy

Metals ◽

10.3390/met10050681 ◽

2020 ◽

Vol 10 (5) ◽

pp. 681 ◽

Cited By ~ 2

Author(s):

Roberto B. Figueiredo ◽

Terence G. Langdon

Keyword(s):

High Pressure ◽

Magnesium Alloy ◽

Grain Boundary ◽

High Pressure Torsion ◽

Grain Boundary Sliding ◽

Grain Structure ◽

Strain Rates ◽

Az91 Magnesium Alloy ◽

Az91 Magnesium ◽

Boundary Sliding

An AZ91 magnesium alloy (Mg-9%, Al-1% Zn) was processed by high-pressure torsion (HPT) after solution-heat treatment. Tensile tests were carried out at 423, 523, and 623 K in the strain rate range of 10−5−10−1 s−1 to evaluate the occurrence of superplasticity. Results showed that HPT processing refined the grain structure in the alloy, and grain sizes smaller than 10 µm were retained up to 623 K. Superplastic elongations were observed at low strain rates at 423 K and at all strain rates at 523 K. An examination of the experiment data showed good agreement with the theoretical prediction for grain-boundary sliding, the rate-controlling mechanism for superplasticity. Elongations in the range of 300–400% were observed at 623 K, attributed to a combination of grain-boundary-sliding and dislocation-climb mechanisms.

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