Deformation kinetics of nanocrystalline nickel

Li, Yujiao; Mueller, Johannes; Höppel, Heinz Werner; Blum, W.

doi:10.1016/j.actamat.2007.06.036

Cited by 76 publications

(38 citation statements)

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“…The value compares with k ε = 7.3 MPa.mm 1/2 for the two points at 298 K of Y.J. Li et al 4 in Fig. 1 1 and so gives indication of an extent of grain boundary weakening having occurred at the higher temperature.…”

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confidence: 99%

“…Li et al 4 on stress-strain and strain rate "jumps" obtained in compression tests as a function of temperature; secondly, for comparable same type strain rate jumps obtained by Mohanty et al 5 in miniature size specimen compression tests; and thirdly, by H. Li et al 6 on strain rate sensitivity measurements made on mostly smaller nm grain size material tested in tension over an exceptionally wide range in strain rates and leading at smallest nm grain sizes to grain size weakening. In each case for the newer measurements, the initial 298 K flow stresses have been multiplied by 3 to calculate the hardness in the manner done by Hughes et al 1 The pair of filled square points in Fig.…”

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confidence: 99%

“…1 came from representative true stress -strain curves reported by Y.J. Li et al 4 at two nano-grain sizes. The material was produced by pulsed electrodeposition.…”

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confidence: 99%

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Unified Hall-Petch description of nano-grain nickel hardness, flow stress and strain rate sensitivity measurements

Armstrong

Balasubramanian²

2017

AIP Advances

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It is shown that: (i) nano-grain nickel flow stress and hardness data at ambient temperature follow a Hall-Petch (H-P) relation over a wide range of grain size; and (ii) accompanying flow stress and strain rate sensitivity measurements follow an analogous H-P relationship for the reciprocal “activation volume”, (1/v*) = (1/A*b) where A* is activation area. Higher temperature flow stress measurements show a greater than expected reduction both in the H-P kε and in v*. The results are connected with smaller nano-grain size (< ∼20 nm) measurements exhibiting grain size weakening behavior that extends to larger grain size when tested at very low imposed strain rates.

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Unified Hall-Petch description of nano-grain nickel hardness, flow stress and strain rate sensitivity measurements

Armstrong

Balasubramanian²

2017

AIP Advances

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“…Macroscopically, the SRS is often measured by uniaxial tension [15][16][17][18][19][20] and compression tests [21,22] on bulk specimens, whereas nanoindentation is widely adopted to measure SRS of small specimens, such as thin films. Figure 1 illustrates the differences between SRS measurement under tension/compression and nanoindentation.…”

Section: Introductionmentioning

confidence: 99%

“…For the C/A multilayer composites, their thermally-activated plastic deformation mechanisms can also be revealed by quantifying their SRS. Thus, various methods have been developed for determining SRS in the past few decades [15][16][17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Thickness-Dependent Strain Rate Sensitivity of Nanolayers via the Nanoindentation Technique

et al. 2018

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Abstract:The strain rate sensitivity (SRS) and dislocation activation volume are two inter-related material properties for understanding thermally-activated plastic deformation, such as creep. For face-centered-cubic metals, SRS normally increases with decreasing grain size, whereas the opposite holds for body-center-cubic metals. However, these findings are applicable to metals with average grain sizes greater than tens of nanometers. Recent studies on mechanical behaviors presented distinct deformation mechanisms in multilayers with individual layer thickness of 20 nanometers or less. It is necessary to estimate the SRS and plastic deformation mechanisms in this regime. Here, we review a new nanoindentation test method that renders reliable hardness measurement insensitive to thermal drift, and its application on SRS of Cu/amorphous-CuNb nanolayers. The new technique is applied to Cu films and returns expected SRS values when compared to conventional tensile test results. The SRS of Cu/amorphous-CuNb nanolayers demonstrates two distinct deformation mechanisms depending on layer thickness: dislocation pileup-dominated and interface-mediated deformation mechanisms.

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Bulk Nanostructured Cu with High Strength and Good Ductility

Zhang¹,

Jiang²,

Lian³

et al. 2008

Adv Eng Mater

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Nanostructured (NS) materials, with average grain sizes typically below 100 nm, are of considerable interest in both scientific and industrial communities. From a scientific viewpoint, interest stems from uncovering novel plastic deformation mechanisms, such as inverse Hall-Petch effect [1,2] and ductile-to-brittle transition. [3,4] From a technological standpoint, it is argued that NS materials may have distinctive mechanical properties in comparison to their coarse-grained (CG) counterparts, resulting in attractive application prospects. In fact, NS materials often exhibit ultrahigh strength and hardness, but at the expense of a much reduced ductility. For example, tensile tests [5][6][7][8][9] on pure NS Cu have shown the yield strength in excess of 400 MPa, which is six times higher than that of CG Cu. However, tensile elongation obtained in these tests is well below 5 %, and it decreases with decreasing the grain size. The disappointingly low ductility can be attributed to the artifacts from processing, the mechanical instability with little or no strain hardening capacity, and low toughness and resistance to crack initiation and propagation. [10] Recently, extensive research has focused on the ductility problem in NS materials and there are indeed examples of optimized strength and ductility in a limited number of cases. Some examples documented their high ductility to the development of bimodal grain size distributions, [11] twin densities [12,13] and strain rate sensitivity. [14][15][16] In other examples, [17][18][19] however, the reasons for enhanced ductility are not clearly defined.In this communication, we fabricated a pure NS Cu through a direct-current eletrodeposition technique. Tensile tests on this NS Cu clearly demonstrated an improved combination of strength and ductility at different strain rates. The mechanism contributing to the high ductility was discussed by the observation on its microstructures as well as the fracture surfaces.The main impurities contents (mass ppm) of the as-deposited NS Cu are listed in Table 1. A relative high content of Pb is measured to be related with the anode material. By X-ray diffraction (XRD) analysis on {111} and {222} peaks with Williamson-Hall integral breadth method, the NS Cu is characterized by an average grain size of ∼ 34 nm and a microstrain of ∼ 0.21 %. Figure 1 shows the transmission electron microscope (TEM) bright-field and corresponding dark-field images of the NS Cu. The grains are mostly equiaxed and have random orientations. Growth twins and dislocations can be found inside some grains. The grain boundaries show no evidence of porosities or contaminations. Many grain boundaries in bright-field images are poorly defined, and they can only be distinguished by dark-field observations. From a statistical analysis of ∼ 400 grains measured from dark-field images, an average grain size of ∼ 90 nm with a lognormal distribution from 30 to 200 nm can be obtained. The main reason for the smaller grain size determined by XRD is that dipoles affect the pe...

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Deformation kinetics of nanocrystalline nickel

Cited by 76 publications

References 50 publications

Unified Hall-Petch description of nano-grain nickel hardness, flow stress and strain rate sensitivity measurements

Unified Hall-Petch description of nano-grain nickel hardness, flow stress and strain rate sensitivity measurements

Thickness-Dependent Strain Rate Sensitivity of Nanolayers via the Nanoindentation Technique

Bulk Nanostructured Cu with High Strength and Good Ductility

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