Mechanically driven grain boundary relaxation: a mechanism for cyclic hardening in nanocrystalline Ni

Rupert, Timothy J.; Schuh, Christopher A.

doi:10.1080/09500839.2011.619507

Cited by 60 publications

(37 citation statements)

References 33 publications

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“…It may therefore be expected that studies that did not minimize GB energy with respect to number of atoms may have inadvertently generated high-energy GBs [32,62]. However, in some cases, the lowest energy GB structures might not be the ones of interest, e.g., when investigating far from equilibrium states [35,87,88]. Sometimes, the atomic-level state of a GB might not even be relevant, e.g., for determining the distribution of intrinsic defects [89,90].…”

Section: Discussionmentioning

confidence: 99%

Non-coherent Cu grain boundaries driven by continuous vacancy loading

Demkowicz

2015

J Mater Sci

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We use atomistic modeling to study the response of three non-coherent grain boundaries (GBs) in Cu to continuous loading with vacancies. Our simulations yield insights into the structure and properties of these boundaries both near and far from thermal equilibrium. We find that GB energies vary periodically as a function of the number of vacancies introduced. Each GB has a characteristic minimum energy state that recurs during continuous vacancy loading, but in general cannot be reached without removing atoms from the boundary. There is no clear correlation of GB energies with GB specific excess volumes or stresses during vacancy loading. However, GB stresses increase monotonically with specific excess volumes. Continuous vacancy loading gives rise to GB migration and shearing, despite the absence of applied loads. Successive vacancies introduced into some of the boundaries accumulate at the cores of what appear to be generalized vacancy dislocation loops. We discuss the implications of these findings for our understanding of grain boundary sink efficiencies under light ion irradiation.

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Section: Discussionmentioning

confidence: 99%

Non-coherent Cu grain boundaries driven by continuous vacancy loading

Demkowicz

2015

J Mater Sci

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“…Previous work has shown that local GB structure can be in a non-equilibrium state, one which contains excess boundary dislocations or free volume [14]. This non-equilibrium structure can be "relaxed" during annealing or deformation [25,42], and the boundary can reach a lower energy state.…”

Section: Methodsmentioning

confidence: 99%

Quantitative tracking of grain structure evolution in a nanocrystalline metal during cyclic loading

Panzarino

Ramos

Rupert

2015

Modelling Simul. Mater. Sci. Eng.

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Molecular dynamics simulations were used to quantify mechanically-induced structural evolution in nanocrystalline Al with an average grain size of 5 nm. A polycrystalline sample was cyclically strained at different temperatures, while a recently developed grain tracking algorithm was used to measure the relative contributions of novel deformation mechanisms such as grain rotation and grain sliding. Sample texture and grain size were also tracked during cycling, to show how nanocrystalline plasticity rearranges overall grain structure and alters the grain boundary network. While no obvious texture is developing during cycling, the processes responsible for plasticity act collectively to alter the interfacial network. Cyclic loading led to the formation of many twin boundaries throughout the sample as well as the occasional coalescence of neighboring grains, with higher temperatures causing more evolution. A temperature-dependent cyclic strengthening effect was observed, demonstrating that both the structure and properties of nanocrystalline metals can be dynamic during loading.2

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“…81 This instability has been attributed to the mobility of high energy grain boundaries formed through electrodeposition, and it has been suggested that if properly conditioned through cyclic loading, the grain boundaries may relax without significant grain coarsening and loss of mechanical strength at ambient temperature. 81,82 However, the application of nominally pure LIGA nickel in load bearing configurations is expected to be quite limited on the basis that most conventional MEMS packaging processes use temperature excursions beyond the threshold for microstructural stability.…”

Section: A Liga Nimentioning

confidence: 99%

Emerging materials for microelectromechanical systems at elevated temperatures

2014

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Extension of microelectromechanical systems (MEMS) into more extreme operating conditions will require a wider range of material properties than are currently available in conventional systems. Successful integration of new materials is dependent on concurrent development of compatible fabrication routes and scale appropriate evaluation techniques. This review focuses on emerging material classes that have potential to replace silicon-based MEMS in elevated temperature applications. Basic silicon mechanical properties and micromachining methods are reviewed to provide context for developing material systems such as silicon carbide, silicon carbonitrides, and several nickel-based alloys. Potential improvements in strength, thermal stability, and reliability are juxtaposed with fabrication, reproducibility, and economic feasibility issues that must also be addressed.

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Mechanically driven grain boundary relaxation: a mechanism for cyclic hardening in nanocrystalline Ni

Cited by 60 publications

References 33 publications

Non-coherent Cu grain boundaries driven by continuous vacancy loading

Non-coherent Cu grain boundaries driven by continuous vacancy loading

Quantitative tracking of grain structure evolution in a nanocrystalline metal during cyclic loading

Emerging materials for microelectromechanical systems at elevated temperatures

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