Shear Strength of Grossly Deformed Cu, Ag, and Au at High Pressures and Temperatures

Riecker, Robert E.; Towle, Laird C.

doi:10.1063/1.1709300

Cited by 26 publications

(6 citation statements)

References 10 publications

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“…15,16 This correlation between friction and silver content can be attributed to the fact that silver facilitates sliding over a range of temperatures due to its low shear strength. 17 We also observed that AgTaO 3 exhibited the lowest friction, slightly lower even than that of the Ta 2 O 5 /Ag film with similar silver content (i.e., 20%), which is consistent with our experimental results.…”

supporting

confidence: 82%

Reconstruction mechanisms of tantalum oxide coatings with low concentrations of silver for high temperature tribological applications

Stone

Gao

Chantharangsi

et al. 2014

Applied Physics Letters

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Silver tantalate (AgTaO 3 ) coatings have been found to exhibit outstanding tribological properties at elevated temperatures. To understand the mechanisms involved in the tribological behavior of the Ag-Ta-O system, tantalum oxide coatings with a small content of silver were produced to investigate the metastable nature of this self-lubricating material. The coatings were produced by unbalanced magnetron sputtering, ball-on-disk wear tested at 750 C, and subsequently characterized by X-ray diffraction, Scanning Auger Nanoprobe, cross-sectional Scanning Electron Microscopy, and Transmission Electron Microscopy. Complementary molecular dynamic simulations were carried out to investigate changes in the chemical and structural properties at the interface due to sliding for films with varying silver content. Both the experimental characterization and the theoretical modeling showed that silver content affects friction and wear, through the role of silver in film reconstruction during sliding. The results suggest that the relative amount of silver may be used to tune film performance for a given application. V C 2014 AIP Publishing LLC. It is well established that high temperature working environments are still a major challenge for the tribology community. Oxidation of the commonly-used solid lubricants, such as MoS 2 and graphite, has hampered their use at elevated temperatures due to the degradation of material properties. 1 Solid lubricants that have been reported in the literature as well as used in industry when the temperature exceeds $300 C include noble metals, alkaline halides, Magn eli phases, and ternary oxides (also termed binary metal oxides).2 These systems usually exhibit friction coefficients in the range of 0.1-0.4, depending on the selected material, working temperature, and load. For more detailed information on the properties of these materials as high temperature solid lubricants, the reader is encouraged to refer to the following review articles. [3][4][5][6] Very recently, silver tantalate (AgTaO 3 ) was reported to be a promising lubricant material at elevated temperatures. 7,8 The measured coefficient of friction (CoF) at 750 C was found to be as low as 0.04-0.06 in two recent studies conducted by our group. Additionally, transmission electron microscopy (TEM) revealed that the AgTaO 3 phase produced clusters of silver surrounded by Ta 2 O 5 near the surface, where the applied stress was presumed to attain its maximum values. These features were reproduced in molecular dynamics (MD) simulations, 8,9 and results indicated that the lubricious nature of AgTaO 3 at high temperatures was enabled by the joint contributions of the hard Ta 2 O 5 phase and lubricious silver clusters in the shear-and temperature-induced surface layer. Theoretical and experimental cross-sectional images of the coatings in the wear track revealed that the presence of Ta 2 O 5 and silver increased dramatically closer to the interface whereas the remainder of the coating consisted primarily of AgTaO 3 with a very small amo...

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supporting

confidence: 82%

Reconstruction mechanisms of tantalum oxide coatings with low concentrations of silver for high temperature tribological applications

Stone

Gao

Chantharangsi

et al. 2014

Applied Physics Letters

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“…[202] The resulting d min = 17.9 nm, the s max = 1.11 GPa, and via MacKenzie's crystal shear model (s max = G/30), with G = 45 GPa, s max = 1.5 GPa. These values appear to be overestimates when compared with experimentally determined maximum shear strengths from rotational diamond anvil cell studies (~100 to 500 MPa), [203] but the smallest predicted grain size of 17.9 nm, and the steady-state experimentally observed values from high-pressure torsion (~35 nm), [204] by cryomilling with no exposure to the liquid (~23 nm) [205] and by cryomilling with exposure to the liquid nitrogen (~24 nm) [206] could be said to ''be in general agreement.'' So where does this bring us in terms of estimating the smallest grain size and its role on strengthening?…”

Section: ½7mentioning

confidence: 62%

Building on Gleiter: The Foundations and Future of Deformation Processing of Nanocrystalline Metals

Mathaudhu

2020

Metall Mater Trans A

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In 1989, fueled by his prior reports and findings, Prof. Herbert Gleiter published a seminal work on the synthesis, processing, and possibilities for nanocrystalline materials. This spark exploded into the field of bulk nanocrystalline metals by severe plastic deformation processing, with the primary driver being attaining the ultimate strength of a metal through refinement of the grain sizes to a level approaching the theoretically possible limits. This paper will briefly explore the historical development of SPD and based on Turnbull's strategy of ''energizing and quenching'' materials to attain a desirable metastable state, present thoughts on incipient-related areas of exploration, including thermal stabilization through solute additions, the role of trace impurities and interstitials, the smallest grain size achievable (both theoretically and practically), and the captivating yet hazy character and role of the grain boundary. Lastly, some new approaches to making and then controlling the behavior of nanocrystalline materials will be presented. At each stage, opportunities for future study will be raised. On the 50th Anniversary of Metallurgical and Materials Transactions A, it is hoped that this report will build off the seed planted by Gleiter and inspire new work and collaborations in the years to come.

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“…Nevertheless, the curve Y d (σ 1 ), as is the case for aluminum and its alloys, is bell-shaped. Studies performed in [43] show that under quasi-static loading at a given temperature, yield strength increases linearly with pressure: Y = Y 0 + αP , where Y 0 is yield strength at atmospheric pressure, and the temperature dependence can be represented as It is therefore apparent that copper undergoes greater hardening under the effect of shock waves than does aluminum.…”

Section: Coppermentioning

confidence: 99%

Dynamic Strength of Materials

Glushak¹,

Tyupanova²,

Bat'kov³

2006

Material Properties Under Intensive Dynamic Loading

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The methods used in practice for the acquisition and interpretation of experimental data pertaining to the resistance of materials to plastic-strain (shearstrength) are based on the concepts of the nature of motion of a material possessing strength and the features of high-rate deformation discussed in Chap. 1. These methods are briefly described below. Additional information on this topic is available to the reader in monographs [1-3], review [4], and the original papers cited in [1-4]. Comparison between the Shock Hugoniot and the Hydrostatic Compression IsothermGiven two assumptions: (1) material strength is isotropic, and (2) the difference between isothermal hydrostatic compression and the mean stress σ ii /3 is small, the dynamic yield strength is calculated to be the difference between the stress σ 1 on the elastic-plastic shock Hugoniot and the pressure P on the hydrostatic compression isotherm (given in terms of specific volume V (or strain ε)) as Y d = 3(σ 1 − P )/2. This approach to the estimation of Y d is limited to cases wherein the stresses σ 1 are relatively low, and the temperature rise during shock compression is modest (resulting in a thermal component of pressure that is low in comparison to the total pressure).For the aluminum alloy Al-2024, [5] recommends that for shock pressures in the 2.7 GPa ≤ σ 1 ≤ 9.4 GPa range, one should use the following relations for σ 1 (ε) (the normal stress component in a plane wave shock) and P (ε) (the hydrostatic compression) in calculations of the dynamic yield strength: σ 1 = 0.18 + 72.06ε − 347.1ε 2 (GPa); P = 75.9ε + 201ε 2 (GPa). This method for the evaluation of Y d , among other things, requires a highly accurate determination of the curves σ 1 (ε) and P (ε) since minor changes in ε can lead to significant changes in σ 1 and P .

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Shear Strength of Grossly Deformed Cu, Ag, and Au at High Pressures and Temperatures

Cited by 26 publications

References 10 publications

Reconstruction mechanisms of tantalum oxide coatings with low concentrations of silver for high temperature tribological applications

Reconstruction mechanisms of tantalum oxide coatings with low concentrations of silver for high temperature tribological applications

Building on Gleiter: The Foundations and Future of Deformation Processing of Nanocrystalline Metals

Dynamic Strength of Materials

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