Microstructure development and hardening during high pressure torsion of commercially pure aluminium: strain reversal experiments and a dislocation based model


Zhang, Jiuwen, Gao, Nong and Starink, Marco J. (2011) Microstructure development and hardening during high pressure torsion of commercially pure aluminium: strain reversal experiments and a dislocation based model. Materials Science and Engineering: A, 528, (6), 2581-2591. (doi:10.1016/j.msea.2010.11.079).

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Description/Abstract

The effect of strain reversal on hardening due to high pressure torsion (HPT) was investigated using commercially pure aluminium. Hardening is lower for cyclic HPT (c-HPT) as compared to monotonic HPT (m-HPT). When using a cycle consisting of a rotation of 90 degree per half cycle, there is only a small increase in hardness if the total amount of turns is increased from 1 to 16. Single reversal HPT (sr-HPT) processing involves torsion in one direction followed by a (smaller) torsion in the opposite direction. It is shown that a small reversal of 0.25 turn (90 degree) reduces hardness drastically, and that decrease is most marked for the centre region. These behaviours and other effects are interpreted in terms of the average density of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs). A model is presented that describes the experimental results well. A key element of the model is the assumption that at the very high strains developed in severe plastic deformation processes such as HPT, the dislocation density reaches a saturation value. The model indicates that the strength / hardness is predominantly due to GNDs and SSDs.

Item Type: Article
ISSNs: 0921-5093 (print)
1873-4936 (electronic)
Keywords: severe plastic deformation (spd), aluminium alloys, high pressure torsion, dislocation, hardness
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TN Mining engineering. Metallurgy
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences > Engineering Materials & Surface Engineering
ePrint ID: 168241
Date Deposited: 25 Nov 2010 14:29
Last Modified: 14 Apr 2014 10:52
Research Funder: EPSRC
Projects:
MEMS COMPONENTS FORMED FROM NANOSTRUCTURAL METALS
Funded by: EPSRC (EP/D00313X/1)
Led by: Nong Gao
1 August 2006 to 31 October 2009
URI: http://eprints.soton.ac.uk/id/eprint/168241

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