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In situ TEM observation of cooperative grain rotations and the Bauschinger effect in nanocrystalline palladium

Kashiwar, Ankush ; Hahn, Horst ; Kübel, Christian (2021)
In situ TEM observation of cooperative grain rotations and the Bauschinger effect in nanocrystalline palladium.
In: Nanomaterials, 11 (2)
doi: 10.3390/nano11020432
Article, Bibliographie

Abstract

We report on cooperative grain rotation accompanied by a strong Bauschinger effect in nanocrystalline (nc) palladium thin film. A thin film of nc Pd was subjected to cyclic loading-unloading using in situ TEM nanomechanics, and the evolving microstructural characteristics were investigated with ADF-STEM imaging and quantitative ACOM-STEM analysis. ADF-STEM imaging revealed a partially reversible rotation of nanosized grains with a strong out-of-plane component during cyclic loading-unloading experiments. Sets of neighboring grains were shown to rotate cooperatively, one after the other, with increasing/decreasing strain. ACOM-STEM in conjunction with these experiments provided information on the crystallographic orientation of the rotating grains at different strain levels. Local Nye tensor analysis showed significantly different geometrically necessary dislocation (GND) density evolution within grains in close proximity, confirming a locally heterogeneous deformation response. The GND density analysis revealed the formation of dislocation pile-ups at grain boundaries (GBs), indicating the generation of back stresses during unloading. A statistical analysis of the orientation changes of individual grains showed the rotation of most grains without global texture development, which fits to both dislocation- and GB sliding-based mechanisms. Overall, our quantitative in situ experimental approach explores the roles of these different deformation mechanisms operating in nanocrystalline metals during cyclic loading.

Item Type: Article
Erschienen: 2021
Creators: Kashiwar, Ankush ; Hahn, Horst ; Kübel, Christian
Type of entry: Bibliographie
Title: In situ TEM observation of cooperative grain rotations and the Bauschinger effect in nanocrystalline palladium
Language: English
Date: February 2021
Publisher: MDPI
Journal or Publication Title: Nanomaterials
Volume of the journal: 11
Issue Number: 2
DOI: 10.3390/nano11020432
Abstract:

We report on cooperative grain rotation accompanied by a strong Bauschinger effect in nanocrystalline (nc) palladium thin film. A thin film of nc Pd was subjected to cyclic loading-unloading using in situ TEM nanomechanics, and the evolving microstructural characteristics were investigated with ADF-STEM imaging and quantitative ACOM-STEM analysis. ADF-STEM imaging revealed a partially reversible rotation of nanosized grains with a strong out-of-plane component during cyclic loading-unloading experiments. Sets of neighboring grains were shown to rotate cooperatively, one after the other, with increasing/decreasing strain. ACOM-STEM in conjunction with these experiments provided information on the crystallographic orientation of the rotating grains at different strain levels. Local Nye tensor analysis showed significantly different geometrically necessary dislocation (GND) density evolution within grains in close proximity, confirming a locally heterogeneous deformation response. The GND density analysis revealed the formation of dislocation pile-ups at grain boundaries (GBs), indicating the generation of back stresses during unloading. A statistical analysis of the orientation changes of individual grains showed the rotation of most grains without global texture development, which fits to both dislocation- and GB sliding-based mechanisms. Overall, our quantitative in situ experimental approach explores the roles of these different deformation mechanisms operating in nanocrystalline metals during cyclic loading.

Uncontrolled Keywords: nanocrystalline metals, nanomechanical behavior, plasticity, thin films, Bauschinger effect, deformation mechanisms, grain rotation, in situ transmission electron microscopy (TEM), automated crystal orientation mapping in STEM (ACOM-STEM)
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > In-situ electron microscopy
Date Deposited: 12 Jun 2024 08:06
Last Modified: 12 Jun 2024 08:06
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