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The significance of strain weakening and self-annealing in a superplastic Bi-Sn eutectic alloy processed by high-pressure torsion

The significance of strain weakening and self-annealing in a superplastic Bi-Sn eutectic alloy processed by high-pressure torsion
The significance of strain weakening and self-annealing in a superplastic Bi-Sn eutectic alloy processed by high-pressure torsion
A cast Bi-Sn eutectic alloy was processed by high-pressure torsion (HPT) at room temperature and stored at room temperature for durations of up to 91 days in order to investigate the effect of self-annealing. The HPT processing produces grain refinement but hardness measurements show there is strain softening with lower microhardness values than in the initial as-cast material and with hardness values that decrease with increasing amounts of imposed torsional strain. This softening is attributed to a loss of precipitates within the Sn and Bi phases during the processing operation. In self-annealing at room temperature, the microhardness increases significantly due to reprecipitation and there is also a minor increase in grain size with increasing time of storage. It is demonstrated by tensile testing that the HPT-processed Bi-Sn alloy exhibits superplastic behavior with elongations of up to >1000% after storage for 35 days and with an associated strain rate sensitivity close to ~0.5. Grain boundary sliding plays an important role in superplastic flow and it is shown that maximum sliding occurs on the Bi-Bi interfaces where this is consistent with estimates of the coefficients for grain boundary diffusion in the Bi-Sn alloy.
Bi-Sn alloy, grain boundary sliding, hardness, high-pressure torsion, superplasticity
1359-6454
245-256
Wang, Chuan Ting
80ad9adf-a9df-49ed-934d-fa64505b920d
He, Yong
479033f6-82b3-4004-88bd-a105203a1c0b
Langdon, Terence G
86e69b4f-e16d-4830-bf8a-5a9c11f0de86
Wang, Chuan Ting
80ad9adf-a9df-49ed-934d-fa64505b920d
He, Yong
479033f6-82b3-4004-88bd-a105203a1c0b
Langdon, Terence G
86e69b4f-e16d-4830-bf8a-5a9c11f0de86

Wang, Chuan Ting, He, Yong and Langdon, Terence G (2020) The significance of strain weakening and self-annealing in a superplastic Bi-Sn eutectic alloy processed by high-pressure torsion. Acta Materialia, 185, 245-256. (doi:10.1016/j.actamat.2019.11.064).

Record type: Article

Abstract

A cast Bi-Sn eutectic alloy was processed by high-pressure torsion (HPT) at room temperature and stored at room temperature for durations of up to 91 days in order to investigate the effect of self-annealing. The HPT processing produces grain refinement but hardness measurements show there is strain softening with lower microhardness values than in the initial as-cast material and with hardness values that decrease with increasing amounts of imposed torsional strain. This softening is attributed to a loss of precipitates within the Sn and Bi phases during the processing operation. In self-annealing at room temperature, the microhardness increases significantly due to reprecipitation and there is also a minor increase in grain size with increasing time of storage. It is demonstrated by tensile testing that the HPT-processed Bi-Sn alloy exhibits superplastic behavior with elongations of up to >1000% after storage for 35 days and with an associated strain rate sensitivity close to ~0.5. Grain boundary sliding plays an important role in superplastic flow and it is shown that maximum sliding occurs on the Bi-Bi interfaces where this is consistent with estimates of the coefficients for grain boundary diffusion in the Bi-Sn alloy.

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More information

Accepted/In Press date: 27 November 2019
e-pub ahead of print date: 29 November 2019
Published date: 15 February 2020
Keywords: Bi-Sn alloy, grain boundary sliding, hardness, high-pressure torsion, superplasticity

Identifiers

Local EPrints ID: 436178
URI: http://eprints.soton.ac.uk/id/eprint/436178
ISSN: 1359-6454
PURE UUID: 952dbd44-726c-4d26-a227-8e74837ffec2
ORCID for Terence G Langdon: ORCID iD orcid.org/0000-0003-3541-9250

Catalogue record

Date deposited: 03 Dec 2019 17:30
Last modified: 22 Nov 2021 02:48

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Contributors

Author: Chuan Ting Wang
Author: Yong He

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