An examination of the saturation microstructures achieved in ultrafine-grained metals processed by high-pressure torsion

Sabbaghianrad, Shima; Wongsa-Ngam, Jittraporn; Kawasaki, Megumi; Langdon, Terence G.

doi:10.1016/j.jmrt.2014.10.002

Cited by 20 publications

(7 citation statements)

References 43 publications

(56 reference statements)

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“…This is in agreement with the plot of hardness values against number of turns of HPT processing. By noting that the numbers of hardness measurements are the same across the diameters of each disk it is possible to simply average these measurements for each processing condition and then to plot the average value of the Vickers microhardness against the total numbers of turns in HPT as reported elsewhere [42]. This confirms that additional grain refinement, and therefore additional hardening, may be achieved by processing the material prior to HPT in order to achieve an even smaller initial grain size.…”

Section: Discussionsupporting

confidence: 55%

Microstructural saturation, hardness stability and superplasticity in ultrafine-grained metals processed by a combination of severe plastic deformation techniques

Sabbaghianrad¹,

Langdon²

2015

LoM

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A commercial Al-7075 aluminum alloy was used to investigate the significance of the saturation hardness and saturation microstructure after processing by high-pressure torsion (HPT) through up to 20 turns or a combination of equal-channel angular pressing (ECAP) for 4 or 8 passes and HPT. The results show additional grain refinement by initially processing the material by ECAP to produce an ultrafine grain size before conducting the HPT. Thus, the grain size immediately prior to the HPT processing controls the saturation microstructure and hardness. Microstructural images reveal a significant grain refinement from elongated grains in the samples prior to processing with an average grain diameter of ~8 μm to equiaxed grains with an average grain size of ~200 nm after processing by a combination of ECAP for 8 passes and HPT through 20 turns. This grain refinement leads to an improvement in the mechanical properties of the Al-7075 alloy. Vickers microhardness tests show a significant increase in the microhardness values of the Al-7075 alloy from Hv≈102 in the annealed samples to Hv≈270 after processing by a combination of ECAP for 8 passes and HPT through 20 turns. Specimens processed by a combination of ECAP and HPT also exhibit excellent superplastic properties with elongations up to >1000% at 673 K.Keywords: aluminum 7075 alloy, equal-channel angular pressing, hardness, high-pressure torsion, severe plastic deformation, superplasticity Насыщение микроструктуры, стабильность твердости и сверхпластичность ультрамелкозернистых металлов, полученных комбинацией методов интенсивной пластической деформацииПромышленный алюминиевый сплав Al-7075 был использован для исследования степени насыщения твердости и насыщения микроструктуры после обработки путем кручения под высоким давлением (КВД) вплоть до 20 оборотов или комбинации равноканального углового прессования (РКУП) в 4 или 8 проходов и КВД. Результаты показывают, что имеет место дополнительное измельчение зерен при предварительной обработке материала путем РКУП, кото-рый создает ультрамелкозернистую структуру перед КВД. Таким образом, размер зерен непосредственно перед КВД определяет микроструктуру и твердость при насыщении. На микроструктурных изображениях выявляется значи-тельное измельчение зерен, их преобразование от удлиненных зерен со средним диаметром около 8 мкм в образцах перед деформацией до равноосных зерен со средним размером около 200 нм после комбинации РКУП в 8 проходов и КВД в 20 оборотов. Это измельчение зерен приводит к улучшению механических свойств сплава Al-7075. Измерения микротвердости по Виккерсу показывают значительное повышение микротвердости сплава Al-7075 от Hv≈102 в отожженных образцах до Hv≈270 после обработки комбинацией РКУП в 8 проходов и КВД в 20 оборотов. Образцы, обработанные комбинацией РКУП и КВД, проявляют также отличные сверхпластические свойства с удлинениями до более чем 1000% при 673 K.

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Section: Discussionsupporting

confidence: 55%

Microstructural saturation, hardness stability and superplasticity in ultrafine-grained metals processed by a combination of severe plastic deformation techniques

Sabbaghianrad¹,

Langdon²

2015

LoM

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“…Subsequently, the hardness seems to increase slowly with equivalent strain. The hardness evolution with radial distance and strain for all samples is similar to the behavior registered in materials classified as being in the "without recovery" condition [14]. According to [15], Figures 8 and 9 indicate that the material has not reached the deformation conditions required to promote a homogeneous mechanical response in terms of hardness (saturation condition).…”

Section: Variations In the Vickers Microhardnesssupporting

confidence: 62%

Experimental and Simulation Studies of Strength and Fracture Behaviors of Wind Turbine Bearing Steel Processed by High Pressure Torsion

et al. 2016

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White structure flaking (WSF) has been found to be one of the failure modes in bearing steels under rolling contacts through the formation of cracks associated with a microstructural change called white etching area (WEA). In the present research, the effects of the high-pressure torsion (HPT) process on the microstructure and mechanical properties of an AISI 52100 alloy are studied. An annealed AISI 52100 was subjected to high-pressure torsion at room temperature under a pressure of up to~6 GPa for up to three turns. Finite-element modeling (FEM) was used to simulate the process under high-pressure torsion and quasi-constrained conditions to reveal the material property changes occurring in HPT. Scanning electron microscopy and microhardness testing after processing were used to investigate the microstructural and mechanical property evolution of the steel. Strain induced microstructural transformations occur and affect the mechanical properties in a similar way to the well-known white etching area (WEA) found beneath the surface of wind turbine bearings. Here, HPT is used to study the feasibility of creating microstructural changes that are similar to WEA. This paper presents the preliminary results of using HPT to produce WEAs.

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“…5 it is apparent that all of the datum points now scatter around a single line and there is a saturation hardness of Hv ≈ 230 at equivalent strains higher than ∼ 180. Similar sets of results are also now available where samples are processed initially by ECAP and then by HPT [24,25].…”

Section: Strengthening By Hptmentioning

confidence: 99%

Strengthening and weakening in the processing of ultrafine-grained metals

Langdon¹

2016

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It is now well established that ultrafine-grained (UFG) metals, with average grain sizes below 1 µm, may be produced by applying severe plastic deformation to bulk metals using processing procedures such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT). Generally, these procedures lead to a significant strengthening in the material but there are some examples where processing by ECAP or HPT produces a significant weakening. This report examines examples of both strengthening and weakening in the processing of UFG metals.K e y w o r d s : equal-channel angular pressing, high-pressure torsion, severe plastic deformation, ultrafine grains

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An examination of the saturation microstructures achieved in ultrafine-grained metals processed by high-pressure torsion

Cited by 20 publications

References 43 publications

Microstructural saturation, hardness stability and superplasticity in ultrafine-grained metals processed by a combination of severe plastic deformation techniques

Microstructural saturation, hardness stability and superplasticity in ultrafine-grained metals processed by a combination of severe plastic deformation techniques

Experimental and Simulation Studies of Strength and Fracture Behaviors of Wind Turbine Bearing Steel Processed by High Pressure Torsion

Strengthening and weakening in the processing of ultrafine-grained metals

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