Key criterion for achieving giant recovery strains in polycrystalline Fe-Mn-Si based shape memory alloys

Peng, H., Wang, G., Wang, S., Chen, J., MacLaren, I. and Wen, Y. (2018) Key criterion for achieving giant recovery strains in polycrystalline Fe-Mn-Si based shape memory alloys. Materials Science and Engineering A: Structural Materials Properties Microstructure and Processing, 712, pp. 37-49. (doi:10.1016/j.msea.2017.11.071)

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Abstract

In this study, it is proposed that coarsening austenitic grains is a key criterion for achieving giant recovery strains in polycrystalline Fe-Mn-Si based shape memory alloys. In order to verify the hypothesis, the relationship between recovery strains and austenitic grain-sizes in cast and processed Fe-Mn-Si based shape memory alloys was investigated. The recovery strain of cast Fe-19Mn-5.5Si-9Cr-4.5Ni alloy with the coarse austenitic grains of 652 µm reached 7.7% while the recovery strain of one with the relatively small austenitic grains of 382 µm was only 5.4%. Moreover, a recovery strain of 5.9%, which is the highest previously published value for solution-treated processed Fe-Mn-Si based shape memory alloys, was obtained by coarsening the austenitic grains through only solution treatment at 1483 K for 360 min in a processed Fe-17Mn-5.5Si-9Cr-5.5Ni-0.12C alloy. However, its recovery strain was still 5.9% after thermo-mechanical treatment consisting of 10% tensile strain at room temperature and annealing at 1073 K for 30 min. This happens because annealing twins play a negative role, refining the austenitic grains, limiting the recovery strains to below 6%. In summary, coarse austenitic grains enable the achievement large recovery strains by two mechanisms. Firstly, the grains are bigger, and consequently there are fewer grain boundaries, and thus their suppressive effects of grain boundaries on stress-induced ε martensitic transformation is reduced. Secondly, coarse austenitic grains are advantageous to introduce ε martensite with single orientation and reduce the collisions of different martensite colonies, especially when the deformation strain is large. As such, the ceiling of recovery strains is dependent on the austenitic grain-sizes.

Item Type:Articles
Additional Information:This work is financially supported by the National Natural Science Foundation of China (Nos. 50871072 and 51401136), the Applied Basic Research Projects of Sichuan Province (No. 2016JY0061) and the International Visiting Program for Excellent Young Scholars of SCU.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Peng, Dr Huabei and MacLaren, Dr Ian
Authors: Peng, H., Wang, G., Wang, S., Chen, J., MacLaren, I., and Wen, Y.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Materials Science and Engineering A: Structural Materials Properties Microstructure and Processing
Publisher:Elsevier
ISSN:0921-5093
ISSN (Online):1873-4936
Published Online:21 November 2017
Copyright Holders:Copyright © 2017 Elsevier B.V.
First Published:First published in Materials Science and Engineering A: Structural Materials Properties Microstructure and Processing 712:37-49
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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