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Title: An origin of functional fatigue of shape memory alloys

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 126; Journal Issue: C; Related Information: CHORUS Timestamp: 2018-02-09 04:13:58; Journal ID: ISSN 1359-6454
Country of Publication:
United States

Citation Formats

Gao, Y., Casalena, L., Bowers, M. L., Noebe, R. D., Mills, M. J., and Wang, Y.. An origin of functional fatigue of shape memory alloys. United States: N. p., 2017. Web. doi:10.1016/j.actamat.2017.01.001.
Gao, Y., Casalena, L., Bowers, M. L., Noebe, R. D., Mills, M. J., & Wang, Y.. An origin of functional fatigue of shape memory alloys. United States. doi:10.1016/j.actamat.2017.01.001.
Gao, Y., Casalena, L., Bowers, M. L., Noebe, R. D., Mills, M. J., and Wang, Y.. Wed . "An origin of functional fatigue of shape memory alloys". United States. doi:10.1016/j.actamat.2017.01.001.
title = {An origin of functional fatigue of shape memory alloys},
author = {Gao, Y. and Casalena, L. and Bowers, M. L. and Noebe, R. D. and Mills, M. J. and Wang, Y.},
abstractNote = {},
doi = {10.1016/j.actamat.2017.01.001},
journal = {Acta Materialia},
number = C,
volume = 126,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2017},
month = {Wed Mar 01 00:00:00 EST 2017}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.actamat.2017.01.001

Citation Metrics:
Cited by: 7works
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Web of Science

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  • It is now well-known that the two-way memory effect (TWME) of shape memory alloys is obtained after a thermomechanical cycling called training. Although this point is well-admitted, many controversies still subsist on the physical origin of this two-memory effect. The explanations of the development of the TWME which are often given are either the presence after training of a low proportion of local stabilized martensite in the parent phase or the presence after training of an internal stress field in the material. Recently, in a systematic study of the two-way memory effect obtained by thermomechanical training cycles under homogeneous tensilemore » constant load, Stalmans et. al. disproved these two previous explanations. Following the study, the most important effect of the dislocation arrays which are introduced during the training is not to develop internal stresses but rather to give rise to a microstructural anisotropy inducing a thermodynamic anisotropy. It means that after training, the crystallographically equivalent martensite variants are no more thermodynamically equivalent. The present paper describes some experimental results obtained by the homogeneous simple shear training of a NiTi shape memory alloy. The experiments have been specifically designed to give new comprehension elements on the existence and the nature of the thermodynamic anisotropy developed during training.« less
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  • A series of Ti-rich Ni-Ti-Pt ternary alloys with 13 to 18 at. pct Pt were processed by vacuum arc melting and characterized for their transformation behavior to identify shape memory alloys (SMA) that undergo transformation between 448 K and 498 K (175 °C and 225 °C) and achieve recoverable strain exceeding 2 pct. From this broader set of compositions, three alloys containing 15.5 to 16.5 at. pct Pt exhibited transformation temperatures in the vicinity of 473 K (200 °C), thus were targeted for more detailed characterization. Preliminary microstructural evaluation of these three compositions revealed a martensitic microstructure with small amountsmore » of Ti 2(Ni,Pt) particles. Room temperature mechanical testing gave a response characteristic of martensitic de-twinning followed by a typical work-hardening behavior to failure. Elevated mechanical testing, performed while the materials were in the austenitic state, revealed yield stresses of approximately 500 MPa and 3.5 pct elongation to failure. Thermal strain recovery characteristics were more carefully investigated with unbiased incremental strain-temperature tests across the 1 to 5 pct strain range, as well as cyclic strain-temperature tests at 3 pct strain. As a result, the unbiased shape recovery results indicated a complicated strain recovery path, dependent on prestrain level, but overall acceptable SMA behavior within the targeted temperature and recoverable strain range.« less
  • The low-cycle fatigue of a TiNi shape memory alloy was investigated by the rotating-bending fatigue tests in air, in water and in silicone oil. (1) The influence of corrosion fatigue in water does not appear in the region of low-cycle fatigue. (2) The temperature rise measured through an infrared thermograph during the fatigue test in air is four times as large as that measured through a thermocouple. (3) The fatigue life at an elevated temperature in air coincides with the fatigue life at the same elevated temperature in water. (4) The shape memory processing temperature does not affect the fatiguemore » life. (5) The fatigue equation is proposed to describe the fatigue life depending on strain amplitude, temperature and frequency. The fatigue life is estimated well by the proposed equation.« less
  • The current investigation proposes a novel method for simultaneous assessment of the electrochemical and structural fatigue properties of nickel-titanium shape memory alloy (NiTi SMA) wires. The design and layout of an in situ electrochemical cell in a custom-made bending rotation fatigue (BRF) test rig is presented. This newly designed test rig allows performing a wide spectrum of experiments for studying the influence of fatigue on corrosion and vice versa. This can be achieved by performing ex situ and/or in situ measurements. The versatility of the combined electrochemical/mechanical test rig is demonstrated by studying the electrochemical behavior of NiTi SMA wiresmore » in 0.9% NaCl electrolyte under load. The ex situ measurements allow addressing various issues, for example, the influence of pre-fatigue on the localized corrosion resistance, or the influence of hydrogen on fatigue life. Ex situ experiments showed that a pre-fatigued wire is more susceptible to localized corrosion. The synergetic effect can be concluded from the polarization studies and specifically from an in situ study of the open circuit potential (OCP) transients, which sensitively react to the elementary repassivation events related to the local failure of the oxide layer. It can also be used as an indicator for identifying the onset of the fatigue failure.« less