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Title: Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires

; ;  [1]
  1. (UNT)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
OSTI Identifier:
Resource Type:
Resource Relation:
Conference: International Conference on Shape Memory and Superelastic Technologies 2015;May 18-22, 2015;Chipping Norton, UK
Country of Publication:
United States

Citation Formats

Carl, Matthew, Zhang, Baozhuo, and Young, Marcus L. Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires. United States: N. p., 2016. Web. doi:10.1007/s40830-016-0073-0.
Carl, Matthew, Zhang, Baozhuo, & Young, Marcus L. Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires. United States. doi:10.1007/s40830-016-0073-0.
Carl, Matthew, Zhang, Baozhuo, and Young, Marcus L. 2016. "Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires". United States. doi:10.1007/s40830-016-0073-0.
title = {Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires},
author = {Carl, Matthew and Zhang, Baozhuo and Young, Marcus L.},
abstractNote = {},
doi = {10.1007/s40830-016-0073-0},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 9

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  • Many technological applications of austenitic shape memory alloys (SMAs) involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity. In this paper, we investigated the effect of mechanical bending of pseudoelastic NiTi SMA wires using high-energy synchrotron radiation X-ray diffraction (SR-XRD). Differential scanning calorimetry was performed to identify the phase transformation temperatures. Scanning electron microscopy images show that micro-cracks in compressive regions of the wire propagate with increasing bend angle, while tensile regions tend not to exhibit crack propagation. SR-XRD patterns were analyzed to study the phase transformation and investigate micromechanical properties. By observing the various diffraction peaks such as the austenite (200) and the martensite (more » $${\bar 1}12$$), ($${\bar 1}03$$), ($${\bar 1}11$$), and (101) planes, intensities and residual strain values exhibit strong anisotropy, depending upon whether the sample is in compression or tension during bending.« less
  • The authors report on the near-reversible strain hysteresis during thermal cycling of a polycrystalline NiTi shape memory alloy at a constant stress that is below the yield strength of the martensite. In situ neutron diffraction experiments are used to demonstrate that the strain hysteresis occurs due to a texture memory effect, where the martensite develops a texture when it is cooled under load from the austenite phase and is thereafter ''remembered.'' Further, the authors quantitatively relate the texture to the strain by developing a calculated strain-texture map or pole figure for the martensite phase, and indicate its applicability in othermore » martensitic transformations.« 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
  • In situ synchrotron X-ray diffraction measurements are used to create two-dimensional maps of elastic strain and texture, averaged over a compact-tension specimen thickness, near a crack tip in a martensitic NiTi alloy. After fatigue crack propagation, the material ahead of the crack and in its wake exhibits a strong texture, which is eliminated by subsequent shape-memory heat treatment, indicating that this texture is due to detwinning, the main deformation mechanism of NiTi. Upon subsequent application of a static tensile stresses, the highly textured zone reappears and grows around the crack tip as the applied stress is increased. At the highestmore » applied stress intensity of 35MPam1/2, large tensile strains are measured ahead of the crack tip and considerable elastic anisotropy is observed. This detwinning zone is similar to the plastic zone produced by dislocation slip present around cracks in other metals. The texture in this zone is not significantly altered after mechanical unloading, despite the development of substantial triaxial compressive residual strains in this zone.« less
  • For a cold-rolled NiTi sheet, the tensile stress-strain curves show a flat stress-plateau during tension along the rolling direction, while under tension along the transverse direction the specimens are quickly strain-hardened and no flat stress-plateau occurred. This shows that the deformation mechanisms of martensite twins are different when loading along different directions. TEM observations show that, in the as-annealed condition, the major type of twins in the martensite phase is {l_angle}011{r_angle} type II twins in the present material. Also present are (001) compound twins and a small amount of (111) type I twins. Deformation details of these three types ofmore » twins are different along rolling and transverse directions. After deformation along the rolling direction to 6% strain, reorientation and de-twinning of the {l_angle}011{r_angle} type II twins have been observed. Instead, a high density of dislocations has been generated inside the {l_angle}011{r_angle} type II twins and de-twinning of the (001) compound twins has been observed. A further crystallographic analysis shows that the shear direction of each type of martensite twins relative to the loading direction is different, which may explain the different deformation behavior of the twins. This may also account for the macroscopical deformation behavior of the material.« less