Grain Growth in Cryomilled Ni Powder during Degassing

Thornton, Jason; Han, Bing; Lavernia, Enrique J.

doi:10.1007/s11661-007-9189-3

Cited by 8 publications

(7 citation statements)

References 24 publications

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“…[32] Nanocrystalline Ni powders with a grain size of approximately 10 nm were prepared by cryomilling commercially pure Ni powders (>99.7 wt %) in liquid nitrogen. [33] The cryomilled Ni powders were placed in stainless steel can and degassed, first at a temperature of 450 8C for 24 hours followed by a second degassing step at a temperature of 810 8C for 2.5 hours. The degassed cans were then QI forged at 800 8C to form bulk dense NS Ni with a purity of 99.3% (Supporting Information Tables 1 and 2), a density of 8.87 g cm À3 (99.6% of Ni's theoretical density), and a multimodal grain size distribution.…”

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confidence: 99%

High Tensile Ductility and Strength in Bulk Nanostructured Nickel

et al. 2008

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Bulk nanostructured (NS) materials have relatively high strength but disappointingly low tensile ductility (elongation to failure) at ambient temperatures. [1][2][3][4] The limited ductility of NS materials has emerged as a particularly challenging issue in the study and application of this novel class of materials. Recently, a variety of strategies aimed at improving the poor ductility of NS materials have been reported; the results reveal varying degrees of success. [5,6] Despite some encouraging reports, the improvements in ductility remain quite limited, usually below 15% for most of the strategies, except possibly for bi-modal Cu (with a ductility of 65%) and ultrafine grained (UFG) Fe-Cr-Ni-Mn steel (ca. 30%). [7,8] In this Communication, we use cryomilling and subsequently quasi-isostatic (QI) forging processes (formerly known as Ceracon forging), to prepare bulk dense multimodal and bimodal NS Ni with tensile ductility of 42% and 49%, and yield strengths of 457 and 312 MPa, respectively. This combination of strength and ductility is much superior to those of the NS Ni prepared by electro-deposition (ED), [9][10][11][12][13][14][15][16] cryorolling, [17] equal-channel angular pressing (ECAP) and high pressure torsion (HPT) methods, [18] and cold drawing. [19] Microstructural analyses suggest that significantly reduced extrinsic processing artifacts, the presence of equilibrium high-angle grain boundaries (including twin boundaries), and multi-/bimodal grain size distributions are responsible for the measured high ductility. The high strength is argued to originate from several sources, including a high density of dislocations, UFGs, and from solid solution strengthening. Compared with other synthesis methods, the synthesis methodology described in the present work has no scale or material limitations, and therefore has important implications in terms of its potential for the large-scale fabrication of bulk NS metals, alloys, and composites that can be used in applications requiring both high ductility and strength. Bulk NS materials are usually synthesized by either a two-step approach involving the synthesis and consolidation of nanoparticles (e.g., via inert-gas condensation) [2,3] or nanocrystalline powders (e.g., via ball milling or cryomilling), [20] or a one-step approach such as severe plastic deformation (SPD). [21] In the case of NS materials prepared by the two-step approach, powder handling can yield extrinsic processing artifacts (such as porosity, incomplete bonding, impurities, and others). It is now well-established that these artifacts, when present, will cause premature failure under tensile stresses, sometimes even before the onset of yielding. [3] In a recent study, the material was consolidated in situ via an approach involving cryomilling followed by room-temperature milling. [22] In this case, the NS Cu prepared by this novel method was reported to have a uniform tensile elongation (strain before necking) of 14% and a high yield strength of 790 MPa. Despite these encouraging results, ...

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High Tensile Ductility and Strength in Bulk Nanostructured Nickel

et al. 2008

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“…A bulk NS Ni sample with porosity and N segregated on the GBs was prepared by cyomilling and quasi-isostatic (QI) forging [27,28]. Nanocrystalline Ni powders with a grain size of approximately 10 nm were prepared by cryomilling commercially pure Ni powders (>99.7 wt.%) in liquid argon.…”

Section: Methodsmentioning

confidence: 99%

“…Chemical composition analysis and density measurement indicate that the forged NS Ni has a purity of 99.2% and a density of 8.51 g/cm 3 (95.5% of Ni theoretical density). The principal impurities are N, Fe and C, which originate from the milling media [27,28], as listed in Table 1. A portion of the forged disk (with a thickness of 10 mm and a diameter of 50 mm) was rolled in thickness reduction of 20% with the rolling direction normal to the forging direction.…”

Section: Methodsmentioning

confidence: 99%

Improving ductility in ultrafine grained nickel with porosity and segregation via deformation

Zhao

Zhan

Topping

et al. 2010

Materials Science and Engineering: A

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“…As can be seen, only pure Si peaks are detected both before and after cryomilling. In contrast, the iron (Fe) content is surprisingly low, in comparison to that generated from the cryomilling of other materials [25,26]. Grain size calculation results determined by full width at half maximum (FWHM) show that the grain size of Si decreases from 125 nm to 25 nm as cyomilling time increases from 6 h to 24 h. Thus, it is suggested that the grain size of the nanocrystalline Si can be well controlled by adjusting the cryomilling time.…”

Section: Controlled Grain Size Of the Cryomilled Nanocrystalline Si Pmentioning

confidence: 99%

Synthesis of Single-Crystalline Silicon Nitride (α-Si₃N₄) Nanowires with Controlled Diameters by Nitriding Cryomilled Nanocrystalline Silicon Powder

et al. 2010

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In the present work, silicon nitride nanowires (SNNWs) have been synthesized via nitriding cryomilled nanocrystalline silicon powder. The silicon powder exhibits a fine polycrystalline structure after the cryomilling process, with an average grain size of 25 to 125 nm at various cryomilling times. The SNNWs that form after the nitridation of the cryomilled silicon powder exhibit single crystal structure and are 20 to 100 nm in diameter and ~10 µm in length. The diameter of the nanowires is in agreement with the grain size of the cryomilled Si powder. Microstructural characterization reveals that the as-synthesized nanowires have a hexagonal structure and their primary growth direction is along the [0001] direction. The formation of the Si−N−Si bond during the cryomilling process, as investigated theoretically with density functional theory, promotes the subsequent synthesis of the α-Si 3 N 4 nanowires. The mechanism for nanowire formation appears to be a vapor-solid (VS) reaction.

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Grain Growth in Cryomilled Ni Powder during Degassing

Cited by 8 publications

References 24 publications

High Tensile Ductility and Strength in Bulk Nanostructured Nickel

High Tensile Ductility and Strength in Bulk Nanostructured Nickel

Improving ductility in ultrafine grained nickel with porosity and segregation via deformation

Synthesis of Single-Crystalline Silicon Nitride (α-Si₃N₄) Nanowires with Controlled Diameters by Nitriding Cryomilled Nanocrystalline Silicon Powder

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Grain Growth in Cryomilled Ni Powder during Degassing

Cited by 8 publications

References 24 publications

High Tensile Ductility and Strength in Bulk Nanostructured Nickel

High Tensile Ductility and Strength in Bulk Nanostructured Nickel

Improving ductility in ultrafine grained nickel with porosity and segregation via deformation

Synthesis of Single-Crystalline Silicon Nitride (α-Si3N4) Nanowires with Controlled Diameters by Nitriding Cryomilled Nanocrystalline Silicon Powder

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Synthesis of Single-Crystalline Silicon Nitride (α-Si₃N₄) Nanowires with Controlled Diameters by Nitriding Cryomilled Nanocrystalline Silicon Powder