Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 528, Issue 6, Pages 2581-2591Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2010.11.079
Keywords
Severe plastic deformation (SPD); Aluminium alloys; High pressure torsion; Dislocation; Hardness
Categories
Funding
- EPRSC [EP/D00313X/1]
- China Scholarship Council (CSC)
- Engineering and Physical Sciences Research Council [EP/D00313X/1] Funding Source: researchfish
- EPSRC [EP/D00313X/1] Funding Source: UKRI
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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 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 degrees) 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. (C) 2010 Elsevier B.V. All rights reserved.
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