Elevated temperature, strain rate jump microcompression of nanocrystalline nickel

Mohanty, Gaurav; Wheeler, Jeffrey M.; Raghavan, R.; Wehrs, Juri; Hasegawa, Masaya; Mischler, S.; Philippe, Laëtitia; Michler, Johann

doi:10.1080/14786435.2014.951709

Cited by 64 publications

(42 citation statements)

References 39 publications

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“…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%

“…Calculations of (b 3 /v*) derived from the measurements of Y.J. Li et al, 4 Mohanty et al 5 and H. Li et al 6 are given in Table I. For H. Li et al, one might note that we used m T in place of their √ 3 factor in determining v*.…”

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confidence: 99%

“…Minor or even negative strain hardening behavior was exhibited in the overall deformation curves. The filled-right-side-up triangle point in the figure for Mohanty et al 5 had been obtained on micropillars of ∼1.5 micron diameter fabricated with a focused ion beam technique. An average 30 nm grain size was determined in this case also by x-ray diffraction.…”

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confidence: 99%

“…The concern relates to the negative strain hardening for the Y.J. Li et al 4 measurements as well as to the grain boundary sliding observations of Mohanty et al 5 The consideration of such grain size weakening at smaller values is often expressed in the generalized constitutive equation 10 (…”

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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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confidence: 99%

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confidence: 99%

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confidence: 99%

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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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“…Furthermore, the value of τIII in the fcc kε is thermallyactivated and so depends on the strain rate in the same manner as applies for the value of σoε. On such basis, an apparent H-P type dependence for the reciprocal value of v* is obtained from both Equation (2) H-P σ0ε and kε terms as (1/v*) = (1/v*)0 + (kε/2mTτCεvC*)ℓ −1/2 (7) Figure 4 shows a compilation of (1/v*) measurements for conventional and nano-scale nickel materials [46][47][48][49]. The measurements follow an H-P type dependence because of the constant value of τCεvC*, at least at small strains [50].…”

Section: Nanograin Size Weakeningmentioning

confidence: 99%

Crystal Engineering for Mechanical Strength at Nano-Scale Dimensions

Armstrong¹

2017

Crystals

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Abstract:The mechanical strengths of nano-scale individual crystal or nanopolycrystalline metals, and other dimensionally-related materials are increased by an order of magnitude or more as compared to those values measured at conventional crystal or polycrystal grain dimensions. An explanation for the result is attributed to the constraint provided at the surface of the crystals or, more importantly, at interfacial boundaries within or between crystals. The effect is most often described in terms either of two size dependencies: an inverse dependence on crystal size because of single dislocation behavior or, within a polycrystalline material, in terms of a reciprocal square root of grain size dependence, designated as a Hall-Petch relationship for the researchers first pointing to the effect for steel and who provided an enduring dislocation pile-up interpretation for the relationship. The current report provides an updated description of such strength properties for iron and steel materials, and describes applications of the relationship to a wider range of materials, including non-ferrous metals, nano-twinned, polyphase, and composite materials. At limiting small nm grain sizes, there is a generally minor strength reversal that is accompanied by an additional order-of-magnitude elevation of an increased strength dependence on deformation rate, thus giving an important emphasis to the strain rate sensitivity property of materials at nano-scale dimensions.

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Elevated and cryogenic temperature micropillar compression of magnesium–niobium multilayer films

et al. 2019

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The mechanical properties of multilayer films consisting of alternating layers of magnesium and niobium are investigated through micropillar compression experiments across a broad range of temperatures. The data collected from the variable temperature micropillar compression tests and strain rate jump tests are used to gain insight into the operative deformation mechanisms within the material. At higher temperatures, diffusion-based deformation mechanisms are shown to determine the plastic behavior of the multilayers. Diffusion occurs more readily along the magnesium-niobium interface than within the bulk, acting as pathway for magnesium diffusion. When individual layer thicknesses are sufficiently small, diffusion can remain the dominant deformation mechanism down to room temperature. Multilayer strengthening models historically rely solely on dislocation-based arguments; therefore, consideration of diffusion-based deformation in nanolaminates with low melting temperature components offers improved understanding of multilayer behavior.

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Elevated temperature, strain rate jump microcompression of nanocrystalline nickel

Cited by 64 publications

References 39 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

Crystal Engineering for Mechanical Strength at Nano-Scale Dimensions

Elevated and cryogenic temperature micropillar compression of magnesium–niobium multilayer films

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