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Shape memory characteristics of a nanocrystalline TiNi alloy processed by HPT followed by post-deformation annealing

Shape memory characteristics of a nanocrystalline TiNi alloy processed by HPT followed by post-deformation annealing
Shape memory characteristics of a nanocrystalline TiNi alloy processed by HPT followed by post-deformation annealing
A martensitic TiNi shape memory alloy was processed by high-pressure torsion (HPT) for 1.5, 10 and 20 turns followed by post-deformation annealing (PDA) at 673 and 773 K for various times in order to study the microstructural evolution during annealing and the shape memory effect (SME). Processing by HPT followed by the optimum PDA leads to an appropriate microstructure for the occurrence of a superior SME which is attributed to the strengthening of the martensitic matrix and grain refinement. A fully martensitic structure (B19' phase) with a very small grain size is ideal for the optimum SME. The results indicate that the nanocrystalline microstructures after PDA contain a martensitic B19' phase together with an R-phase and this latter phase diminishes the SME. Applying a higher annealing temperature or longer annealing time may remove the R-phase but also reduce the SME due to grain growth and the consequent decrease in the strength of the material. The results show the optimum procedure is a short-term anneal for 10 min at 673 K or only 1.5 min at 773 K after 1.5 turns of HPT processing to produce a maximum recovered strain of ~8.4% which shows more than 50% improvement compared with the solution-annealed condition.
0921-5093
445-452
Shahmir, Hamed
9d330616-d35d-4db0-96e8-26195ae1c511
Nili-Ahmadabadi, Mahmoud
74c5b0be-a73e-40fe-bc6e-8450bc0eeaf7
Huang, Yi
9f4df815-51c1-4ee8-ad63-a92bf997103e
Jung, Jai Myun
93d9f89f-6c23-4cd4-b541-676885c298ed
Kim, Hyoung Seop
762e00dc-3fa4-49ec-85d5-0f5bab01399b
Langdon, Terence G.
86e69b4f-e16d-4830-bf8a-5a9c11f0de86
Shahmir, Hamed
9d330616-d35d-4db0-96e8-26195ae1c511
Nili-Ahmadabadi, Mahmoud
74c5b0be-a73e-40fe-bc6e-8450bc0eeaf7
Huang, Yi
9f4df815-51c1-4ee8-ad63-a92bf997103e
Jung, Jai Myun
93d9f89f-6c23-4cd4-b541-676885c298ed
Kim, Hyoung Seop
762e00dc-3fa4-49ec-85d5-0f5bab01399b
Langdon, Terence G.
86e69b4f-e16d-4830-bf8a-5a9c11f0de86

Shahmir, Hamed, Nili-Ahmadabadi, Mahmoud, Huang, Yi, Jung, Jai Myun, Kim, Hyoung Seop and Langdon, Terence G. (2018) Shape memory characteristics of a nanocrystalline TiNi alloy processed by HPT followed by post-deformation annealing. Materials Science and Engineering: A, 734, 445-452. (doi:10.1016/j.msea.2018.08.019).

Record type: Article

Abstract

A martensitic TiNi shape memory alloy was processed by high-pressure torsion (HPT) for 1.5, 10 and 20 turns followed by post-deformation annealing (PDA) at 673 and 773 K for various times in order to study the microstructural evolution during annealing and the shape memory effect (SME). Processing by HPT followed by the optimum PDA leads to an appropriate microstructure for the occurrence of a superior SME which is attributed to the strengthening of the martensitic matrix and grain refinement. A fully martensitic structure (B19' phase) with a very small grain size is ideal for the optimum SME. The results indicate that the nanocrystalline microstructures after PDA contain a martensitic B19' phase together with an R-phase and this latter phase diminishes the SME. Applying a higher annealing temperature or longer annealing time may remove the R-phase but also reduce the SME due to grain growth and the consequent decrease in the strength of the material. The results show the optimum procedure is a short-term anneal for 10 min at 673 K or only 1.5 min at 773 K after 1.5 turns of HPT processing to produce a maximum recovered strain of ~8.4% which shows more than 50% improvement compared with the solution-annealed condition.

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Hamed-MSE 2018-accepted manuscript - Accepted Manuscript
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Accepted/In Press date: 6 August 2018
e-pub ahead of print date: 7 August 2018
Published date: 12 September 2018

Identifiers

Local EPrints ID: 423031
URI: http://eprints.soton.ac.uk/id/eprint/423031
ISSN: 0921-5093
PURE UUID: 1b75fce5-b65d-4e02-8eae-22852ce497a9
ORCID for Yi Huang: ORCID iD orcid.org/0000-0001-9259-8123
ORCID for Terence G. Langdon: ORCID iD orcid.org/0000-0003-3541-9250

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Date deposited: 10 Aug 2018 16:30
Last modified: 17 Dec 2019 05:16

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Contributors

Author: Hamed Shahmir
Author: Mahmoud Nili-Ahmadabadi
Author: Yi Huang ORCID iD
Author: Jai Myun Jung
Author: Hyoung Seop Kim

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