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Inverse Hall–Petch behaviour in an AZ91 alloy and in an AZ91–Al2O3 composite consolidated by high-pressure torsion

Inverse Hall–Petch behaviour in an AZ91 alloy and in an AZ91–Al2O3 composite consolidated by high-pressure torsion
Inverse Hall–Petch behaviour in an AZ91 alloy and in an AZ91–Al2O3 composite consolidated by high-pressure torsion
High-pressure torsion (HPT) is a significant procedure for achieving substantial grain refinement but it may be used also to consolidate metallic particles to form bulk samples or composites where two (or more) different phases are mixed and consolidated. Herein, the consolidation of particles of the magnesium AZ91 alloy and a composite with an AZ91 matrix combined with 1% alumina powder is investigated. The results show that it is possible to fully consolidate this alloy after a large number of turns. As a consequence of the severe plastic deformation, the grain structure is significantly refined, with average grain sizes of 116 and 98 nm in the unreinforced alloy after 20 or 50 HPT turns and 76 nm in the composite after 50 HPT turns, respectively. This grain refinement is associated with a decrease in hardness and an increase in the strain rate sensitivity due to the onset of a grain boundary diffusion–assisted creep mechanism at room temperature. The results are consistent with the theoretical prediction of a breakdown in the Hall–Petch relationship at very small grain sizes.
Hall–Petch breakdown, composites, high-pressure torsion, magnesium, particle consolidation
1438-1656
Castro, Moara M.
cb6729d8-fd38-46a4-91e3-a87da53d0e99
Figueiredo, R.B.
1b4f5fa6-b201-4435-8f5e-13833fc8d504
Pereira, Pedro Henrique R.
f033a8a6-ddad-4f6a-91ec-521a3358e4c2
Isaac, Augusta C.
8bbd9d2d-a43b-442f-8d29-ae1a319ca616
Langdon, Terence G.
86e69b4f-e16d-4830-bf8a-5a9c11f0de86
Castro, Moara M.
cb6729d8-fd38-46a4-91e3-a87da53d0e99
Figueiredo, R.B.
1b4f5fa6-b201-4435-8f5e-13833fc8d504
Pereira, Pedro Henrique R.
f033a8a6-ddad-4f6a-91ec-521a3358e4c2
Isaac, Augusta C.
8bbd9d2d-a43b-442f-8d29-ae1a319ca616
Langdon, Terence G.
86e69b4f-e16d-4830-bf8a-5a9c11f0de86

Castro, Moara M., Figueiredo, R.B., Pereira, Pedro Henrique R., Isaac, Augusta C. and Langdon, Terence G. (2020) Inverse Hall–Petch behaviour in an AZ91 alloy and in an AZ91–Al2O3 composite consolidated by high-pressure torsion. Advanced Engineering Materials, 22 (10), [1900894]. (doi:10.1002/adem.201900894).

Record type: Article

Abstract

High-pressure torsion (HPT) is a significant procedure for achieving substantial grain refinement but it may be used also to consolidate metallic particles to form bulk samples or composites where two (or more) different phases are mixed and consolidated. Herein, the consolidation of particles of the magnesium AZ91 alloy and a composite with an AZ91 matrix combined with 1% alumina powder is investigated. The results show that it is possible to fully consolidate this alloy after a large number of turns. As a consequence of the severe plastic deformation, the grain structure is significantly refined, with average grain sizes of 116 and 98 nm in the unreinforced alloy after 20 or 50 HPT turns and 76 nm in the composite after 50 HPT turns, respectively. This grain refinement is associated with a decrease in hardness and an increase in the strain rate sensitivity due to the onset of a grain boundary diffusion–assisted creep mechanism at room temperature. The results are consistent with the theoretical prediction of a breakdown in the Hall–Petch relationship at very small grain sizes.

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RBF-Castro 2019 AEM SFMC manuscript revised TGL - Accepted Manuscript
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Accepted/In Press date: 18 October 2019
e-pub ahead of print date: 31 October 2019
Published date: 31 October 2020
Keywords: Hall–Petch breakdown, composites, high-pressure torsion, magnesium, particle consolidation

Identifiers

Local EPrints ID: 445204
URI: http://eprints.soton.ac.uk/id/eprint/445204
ISSN: 1438-1656
PURE UUID: 37f2c807-f3cc-4b25-8dc1-3d62d6b59e30
ORCID for Terence G. Langdon: ORCID iD orcid.org/0000-0003-3541-9250

Catalogue record

Date deposited: 25 Nov 2020 17:31
Last modified: 26 Nov 2021 02:46

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Contributors

Author: Moara M. Castro
Author: R.B. Figueiredo
Author: Pedro Henrique R. Pereira
Author: Augusta C. Isaac

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