Microstructural characteristics of nickel processed to ultrahigh strains by high-pressure torsion

Zhilyaev, Alexander P.; Gimazov, A.A.; Soshnikova, E.P.; Révész, Ádám; Langdon, Terence G.

doi:10.1016/j.msea.2007.12.031

Cited by 37 publications

(28 citation statements)

References 27 publications

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“…The copper subjected to machining and HPT contained the highest fraction of highangle boundaries of *69%, but there was no evidence of any run-away grain growth in this sample or in any of the other samples subjected to multiple SPD processing. This result therefore confirms recent experimental data for commercial purity aluminum [20] and pure nickel [21], where HPT straining was continued for 20 whole revolutions.…”

Section: Experimental Materials and Proceduressupporting

confidence: 91%

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An evaluation of microstructure and microhardness in copper subjected to ultra-high strains

et al. 2008

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The microstructure and microhardness of copper subjected to large strains either using one or a combination of severe plastic deformation (SPD) processing techniques was evaluated. The individual SPD techniques used include equal-channel angular pressing (ECAP), high-pressure torsion (HPT), and chip formation during machining (M). Microstructural characterization using orientation imaging microscopy provided detailed information on the grain sizes and misorientation statistics after different processing routes. Vickers indentation analysis was used to evaluate the hardness of the deformed samples. The results show that excellent microstructures and properties are achieved when these three processes are used in combination, including grain sizes in the range of *0.2-0.3 lm and hardness values up to [1,900 MPa.

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Section: Experimental Materials and Proceduressupporting

confidence: 91%

“…In earlier studies, the dislocation density after multiple SPD processing was shown to be higher than the density recorded after a single SPD process [16,21]. Furthermore, samples of an Al-7% Si alloy were shown earlier to experience an estimated temperature rise of up to *120°C in HPT processing [22].…”

Section: Experimental Materials and Proceduresmentioning

confidence: 94%

An evaluation of microstructure and microhardness in copper subjected to ultra-high strains

et al. 2008

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“…Full details of the experimental procedure for rapid quenching were described earlier [12]. Briefly, ribbons of pure nickel were prepared by melt spinning under an argon atmosphere using a copper wheel with a rotation speed of ~10 3 revolutions per minute.…”

Section: Experimental Procedures and Materialsmentioning

confidence: 99%

“…Final specimens had a disk shape of ~10 mm in diameters and about 0.5 mm in thickness. Further details can be found elsewhere [3,12].…”

Section: Experimental Procedures and Materialsmentioning

confidence: 99%

“…Another method of processing ultrafine-grained structure is the HPT consolidation of rapid quenched (RQ) nickel ribbons. It was shown earlier [12] that bulk specimens with fine structure of grain size of about 0.2 µm or less can be processed by this method. The aim of this paper to study tensile properties of HPT consolidated RQ nickel at elevated temperatures and discuss the results obtained in light of possibility to achieve superplacticity in pure metals.…”

Section: Introductionmentioning

confidence: 98%

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Enhanced plasticity and superplasticity of ultrafine-grained nickel

Zhilyaev¹

2015

LoM

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Although superplasticity has intensively been studied for half century, few observations have been reported for pure metals due to fast grain growth at temperatures required for superplasticity. With developing of nanocrystalline materials, there was a hope that superplasticity could be obtained in a number of pure metals. Indeed, low temperature superplasticity in pure nickel was reported in pioneering work in 1999, later superplastic feature of nanonickel was attributed to sulfur presence in grain boundaries. Recently, it was concluded that superplasticity it is not related to the presence of sulfur at grain boundaries or a liquid phase at grain boundaries. Thereby, the phenomenon of superplasticity in pure metals is still far away for our understanding and it requires future work. This report is devoted to reassessment of superplastic behavior of nano-nickel and it provides new results on enhanced plasticity of pure nickel processed by HPT consolidation of rapid quenched ribbons. Bulk ultrafine-grained nickel was successfully processed by RT consolidation of rapid quenched ribbons using high-pressure torsion. RQ nickel possesses equiaxed grain structure with mean grain size of 1−2 µm showing well defined grain boundaries. Upon HPT consolidation mean grain size of ~0.2 µm and high dislocation density have been achieved. However, consolidated Ni specimens show enhanced plasticity >140% at testing temperature of 450°C and strain rate of 10 -3 s -1. No superplastic regime has been attained for given testing conditions. Keywords: nickel, superplasticity, electrodeposition, rapid quenched ribbons, high-pressure torsion, consolidation Повышенная пластичность и сверхпластичность ультрамелкозернистого никеляХотя сверхпластичность интенсивно исследовалась в течение полувека, только небольшое количество данных было опубликовано для случая чистых металлов ввиду быстрого роста зерен в них при температурах, необходимых для сверхпластичности. С разработкой нанокристаллических материалов появилась надежда, что сверхпластичность может быть получена в ряде чистых металлов. Действительно, низкотемпературная сверхпластичность была обна-ружена в пионерской работе в 1999 г.; позднее сверхпластическое поведение наноникеля было объяснено наличием серы в границах зерен. Недавно было выяснено, что сверхпластичность не связана с серой в границах зерен или жид-кой фазой в границах зерен. Таким образом, явление сверхпластичности в чистых металлах все еще далеко от пони-мания и требует дальнейшего исследования. Данная работа посвящена пересмотру сверхпластического поведения наноникеля и приводит новые данные о повышенной пластичности чистого никеля полученного путем консолида-ции методом кручения под высоким давлением (КВД) быстрозакаленных лент. Путем консолидации быстрозака-ленных лент методом КВД был получен объемный ультрамелкозернистый никель. Быстрозакаленный никель имеет равноосную зеренную структуру со средним размером зерен 1−2 мкм и хорошо сформированными границами зе-рен. После консолидации КВД достигнут средний размер зерен ок...

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