The effect of grain size on strain rate sensitivity and activation volume – from nano to ufg nickel

Vehoff, H.; Lemaire, Delphine; Schüler, Kerstin; Waschkies, Thomas; Yang, Bo

doi:10.3139/146.101464

Cited by 48 publications

(16 citation statements)

References 31 publications

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“…Such a large m* value indicate that the deformation mechanism of our NS Cu is controlled by dislocation process, and the decreasing of m* with strain indicates an increasing in dislocation density. [23,24] This is in agreement with the work hardening behavior shown in Figure 2(b).…”

supporting

confidence: 80%

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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supporting

confidence: 80%

Bulk Nanostructured Cu with High Strength and Good Ductility

Zhang¹,

Jiang²,

Lian³

et al. 2008

Adv Eng Mater

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“…59 Furthermore, multiple deformation mechanisms may be active simultaneously, so the apparent volume may not be indicative of a single rate-controlling deformation mechanism. The room-temperature activation volumes for deformation of nanocrystalline nickel from the current study and the literature 16,24,31,60,61 are summarized in Table I. The current study reveals nearly identical values of $10 b 3 for all the different loading cases for the nanocrystalline nickel sample.…”

Section: Apparent Activation Volumesupporting

confidence: 54%

Comparison of In Situ Micromechanical Strain-Rate Sensitivity Measurement Techniques

Wehrs

Mohanty

Guillonneau

et al. 2015

JOM

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“…However, nanoindentation testing is a useful tool for studying these effects on a local scale, allowing a detailed localized analysis of the deformation processes. 7 Besides focusing on the local determination of the strain-rate sensitivity, [8][9][10][11] the development of reliable nanoindentation creep experiments has gained much attention over the last decades. In literature, references can be found relating to studies of different indentation procedures concerning the relationship between indentation strain-rate and hardness.…”

Section: Introductionmentioning

confidence: 99%

An improved long-term nanoindentation creep testing approach for studying the local deformation processes in nanocrystalline metals at room and elevated temperatures

et al. 2013

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The strain-rate sensitivity of ultrafine-grained aluminum (Al) and nanocrystalline nickel (Ni) is studied with an improved nanoindentation creep method. Using the dynamic contact stiffness thermal drift influences can be minimized and reliable creep data can be obtained from nanoindentation creep experiments even at enhanced temperatures and up to 10 h. For face-centered cubic (fcc) metals it was found that the creep behavior is strongly influenced by the microstructure, as nanocrystalline (nc) as well as ultrafine-grained (ufg) samples show lower stress exponents when compared with their coarse-grained (cg) counterparts. The indentation creep behavior resembles a power-law behavior with stress exponents n being ; 20 at room temperature. For higher temperatures the stress exponents of ufg-Al and nc-Ni decrease down to n ; 5. These locally determined stress exponents are similar to the macroscopic exponents, indicating that similar deformation mechanisms are acting during indentation and macroscopic deformation. Grain boundary sliding found around the residual indentations is related to the motion of unconstrained surface grains.

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The effect of grain size on strain rate sensitivity and activation volume – from nano to ufg nickel

Cited by 48 publications

References 31 publications

Bulk Nanostructured Cu with High Strength and Good Ductility

Bulk Nanostructured Cu with High Strength and Good Ductility

Comparison of In Situ Micromechanical Strain-Rate Sensitivity Measurement Techniques

An improved long-term nanoindentation creep testing approach for studying the local deformation processes in nanocrystalline metals at room and elevated temperatures

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