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Microstructure-dependent deformation behaviour of bcc-metals – indentation size effect and strain rate sensitivity

Maier, Verena and Schunk, Christopher and Göken, Mathias and Durst, Karsten (2015):
Microstructure-dependent deformation behaviour of bcc-metals – indentation size effect and strain rate sensitivity.
In: Philosophical Magazine, TAYLOR & FRANCIS LTD, England, pp. 1766-1779, 95, (16-18), ISSN 1478-6435, [Online-Edition: http://dx.doi.org/10.1080/14786435.2014.982741],
[Article]

Abstract

In this work, the indentation size effect and the influence of the microstructure on the time-dependent deformation behaviour of body-centred cubic (bcc) metals are studied by performing nanoindentation strain rate jump tests at room temperature. During these experiments, the strain rate is abruptly changed, and from the resulting hardness difference the local strain rate sensitivity has been derived. Single-crystalline materials exhibit a strong indentation size effect; ultrafine-grained metals have nearly a depth-independent hardness. Tungsten as a bcc metal shows the opposite behaviour as generally found for face-centered cubic metals. While for UFG-W only slightly enhanced strain rate sensitivity was observed, SX-W exhibits a pronounced influence of the strain rate on the resulting hardness at room temperature. This is due to the effects of the high lattice friction of bcc metals at low temperatures, where the thermally activated motion of screw dislocations is the dominating deformation mechanisms, which causes the enhanced strain rate sensitivity. For the SX-materials, it was found that the degree of the indentation size effect directly correlates with the homologous testing temperature and thus, the material specific parameter of the critical temperature T-c. However, for the resultant strain rate sensitivity no depth-dependent change was found.

Item Type: Article
Erschienen: 2015
Creators: Maier, Verena and Schunk, Christopher and Göken, Mathias and Durst, Karsten
Title: Microstructure-dependent deformation behaviour of bcc-metals – indentation size effect and strain rate sensitivity
Language: English
Abstract:

In this work, the indentation size effect and the influence of the microstructure on the time-dependent deformation behaviour of body-centred cubic (bcc) metals are studied by performing nanoindentation strain rate jump tests at room temperature. During these experiments, the strain rate is abruptly changed, and from the resulting hardness difference the local strain rate sensitivity has been derived. Single-crystalline materials exhibit a strong indentation size effect; ultrafine-grained metals have nearly a depth-independent hardness. Tungsten as a bcc metal shows the opposite behaviour as generally found for face-centered cubic metals. While for UFG-W only slightly enhanced strain rate sensitivity was observed, SX-W exhibits a pronounced influence of the strain rate on the resulting hardness at room temperature. This is due to the effects of the high lattice friction of bcc metals at low temperatures, where the thermally activated motion of screw dislocations is the dominating deformation mechanisms, which causes the enhanced strain rate sensitivity. For the SX-materials, it was found that the degree of the indentation size effect directly correlates with the homologous testing temperature and thus, the material specific parameter of the critical temperature T-c. However, for the resultant strain rate sensitivity no depth-dependent change was found.

Journal or Publication Title: Philosophical Magazine
Volume: 95
Number: 16-18
Publisher: TAYLOR & FRANCIS LTD, England
Uncontrolled Keywords: nanoindentation, bcc metals, deformation behaviour, strain rate sensitivity, indentation size effect
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Physical Metallurgy
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 08 Mar 2016 09:53
Official URL: http://dx.doi.org/10.1080/14786435.2014.982741
Identification Number: doi:10.1080/14786435.2014.982741
Funders: Financial support was provided by the German Research Council (DFG), which, within the framework of its 'Excellence Initiative' supports the Cluster of Excellence "Engineering of Advanced Materials" at the University of Erlangen-Nurnberg., Financial support was provided at the Montanuniversitat Leoben by the Zukunftsfond Steiermark within the project 6019 "Nanofatigue".
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