Damping Characteristics of Ti50Ni50- xCu x (x = 0~30 at.%) Shape Memory Alloys at a Low Frequency

Chen Chien; Shyi-Kaan Wu; Shih-Hang Chang

doi:10.3390/ma7064574

Damping Characteristics of Ti₅₀Ni_{50- x}Cu _x (x = 0~30 at.%) Shape Memory Alloys at a Low Frequency

Materials (Basel). 2014 Jun 16;7(6):4574-4586. doi: 10.3390/ma7064574.

Authors

Chen Chien¹, Shyi-Kaan Wu^{2

3}, Shih-Hang Chang⁴

Affiliations

¹ Department of Materials Science and Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 106, Taiwan. d01527004@ntu.edu.tw.
² Department of Materials Science and Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 106, Taiwan. skw@ntu.edu.tw.
³ Department of Mechanical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 106, Taiwan. skw@ntu.edu.tw.
⁴ Department of Chemical and Materials Engineering, National I-Lan University, No. 1, Sec. 1, Shen-Lung Road, I-Lan 260, Taiwan. shchang@niu.edu.tw.

Abstract

The damping characteristics of Ti₅₀Ni_50-xCu_x (x = 0~30 at.%) shape memory alloys (SMAs) at a low frequency have been studied using a dynamic mechanical analyzer. The magnitude of the tan δ value and the values of the storage modulus (E₀) softening/hardening and the strain variation exhibited in B2↔B19 transformation are all higher than those in B2↔B19' transformation. The larger E₀ softening/hardening in B2↔B19 can induce higher strain variation in this transformation. It is suggested that the greater mobility of the twin boundaries and the larger magnitude of the strain variation both cause the higher tan δ value exhibited in B2↔B19 transformation, as compared with B2↔B19' transformation. In comparison with that in B19' martensite, the E₀ value in B19 martensite is low and not affected so greatly by changes in temperature. Relaxation peaks are observed in B19' martensite, but not in B19 martensite, because the latter has rare twinned variants. The activation energy of the relaxation peak is calculated and found to increase as the Cu-content increases in these SMAs.

Keywords: damping properties; martensitic transformation; relaxation peak; shape memory alloys; twins.