In Situ Observation of Thermoelastic Martensitic Transformation of Cu-Al-Mn Cryogenic Shape Memory Alloy with Compressive Stress

Zhenyu Bian; Jian Song; Pingping Liu; Farong Wan; Yu Lei; Qicong Wang; Shanwu Yang; Qian Zhan; Liubiao Chen; Junjie Wang

doi:10.3390/ma15113794

In Situ Observation of Thermoelastic Martensitic Transformation of Cu-Al-Mn Cryogenic Shape Memory Alloy with Compressive Stress

Materials (Basel). 2022 May 26;15(11):3794. doi: 10.3390/ma15113794.

Authors

Zhenyu Bian^{1

2}, Jian Song¹, Pingping Liu¹, Farong Wan¹, Yu Lei³, Qicong Wang¹, Shanwu Yang¹, Qian Zhan¹, Liubiao Chen⁴, Junjie Wang⁴

Affiliations

¹ School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China.
² China Classification Society Certification Co., Ltd., Beijing 100006, China.
³ Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan.
⁴ Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China.

Abstract

The thermoelastic martensitic transformation and its reverse transformation of the Cu-Al-Mn cryogenic shape memory alloy, both with and without compressive stress, has been dynamically in situ observed. During the process of thermoelastic martensitic transformation, martensite nucleates and gradually grow up as they cool, and shrink to disappearance as they heat. The order of martensite disappearance is just opposite to that of their formation. Observations of the self-accommodation of martensite variants, which were carried out by using a low temperature metallographic in situ observation apparatus, showed that the variants could interact with each other. The results of in situ synchrotron radiation X-ray and metallographic observation also suggested there were some residual austenites, even if the temperature was below M_f, which means the martensitic transformation could not be 100% accomplished. The external compressive stress would promote the preferential formation of martensite with some orientation, and also hinder the formation of martensite with other nonequivalent directions. The possible mechanism of the martensitic reverse transformation is discussed.

Keywords: compressive stress; cryogenic metallography; cryogenic shape memory alloys; in situ observation; residual austenite; synchrotron radiation.

Grants and funding

This work was funded by the National Magnetic Confinement Fusion Program (grant no. 2022YFE03110003 and 2019YFE03130002), the Fundamental Research Funds for the Central Universities, with grant nos. FRF-IDRY-20-002 and FRF-GF-20-02A, and the National Natural Science Foundation of China (grant nos. 51971019 and 51971030).