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Title: Porous shape-memory NiTi-Nb with microchannel arrays

Authors:
; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1323580
Grant/Contract Number:
SC0010594
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 115; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-05 09:19:31; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Country of Publication:
United States
Language:
English

Citation Formats

Bewerse, C., Brinson, L. C., and Dunand, D. C. Porous shape-memory NiTi-Nb with microchannel arrays. United States: N. p., 2016. Web. doi:10.1016/j.actamat.2016.05.056.
Bewerse, C., Brinson, L. C., & Dunand, D. C. Porous shape-memory NiTi-Nb with microchannel arrays. United States. doi:10.1016/j.actamat.2016.05.056.
Bewerse, C., Brinson, L. C., and Dunand, D. C. 2016. "Porous shape-memory NiTi-Nb with microchannel arrays". United States. doi:10.1016/j.actamat.2016.05.056.
@article{osti_1323580,
title = {Porous shape-memory NiTi-Nb with microchannel arrays},
author = {Bewerse, C. and Brinson, L. C. and Dunand, D. C.},
abstractNote = {},
doi = {10.1016/j.actamat.2016.05.056},
journal = {Acta Materialia},
number = C,
volume = 115,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.actamat.2016.05.056

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  • The transformation behavior of near-equiatomic NiTi containing 0, 10, and 20 vol pct TiC particulates is investigated by dilatometry. Undeformed composites exhibit a macroscopic transformation strain larger than predicted when assuming that the elastic transformation mismatch between the matrix and the particulates is unrelaxed, indicating that the mismatch is partially accommodated by matrix twinning during transformation. The thermal recovery behavior of unreinforced NiTi which was deformed primarily by twinning in the martensite phase shows that plastic deformation by slip increases with increasing prestrain, leading to (1) a decrease of the shape-memory strain on heating, (2) an increase of the two-waymore » shape-memory strain on cooling, (3) a widening of the temperature interval over which the strain recovery occurs on heating, and (4) an increase of the transformation temperature hysteresis. For NiTi composites, the recovery behavior indicates that most of the mismatch during mechanical deformation between the TiC particulates and the NiTi matrix is relaxed by matrix twinning. However, some relaxation takes place by matrix slip, resulting in the following trends with increasing TiC content at constant prestrain: (1) decrease of the shape-memory strain on heating, (2) enhancement of the two-way shape-memory strain on cooling, and (3) broadening of the transformation interval on heating.« less
  • Neutron diffraction measurements of internal elastic strains and crystallographic orientation were performed during compressive deformation of martensitic NiTi containing 0 vol pct and 20 vol pct TiC particles. For bulk NiTi, some twinning takes place upon initial loading below the apparent yield stress, resulting in a low apparent Young`s modulus; for reinforced NiTi, the elastic mismatch from the stiff particles enhances this effect. However, elastic load transfer between matrix and reinforcement takes place above and below the composite apparent yield stress, in good agreement with continuum mechanics predictions. Macroscopic plastic deformation occurs by matrix twinning, whereby (1 0 0) planesmore » tend to align perpendicular to the stress axis. The elastic TiC particles do not alter the overall twinning behavior, indicating that the mismatch stresses associated with NiTi plastic deformation are fully relaxed by localized twinning at the interface between the matrix and the reinforcement. For both bulk and reinforced NiTi, partial reverse twinning takes place upon unloading, as indicated by a Bauschinger effect followed by rubberlike behavior, resulting in very low residual stresses in the unloaded condition. Shape-memory heat treatment leads to further recovery of the preferred orientation and very low residual stresses, as a result of self-accommodation during the phase transformations. It is concluded that, except for elastic load transfer, the thermal, transformation, and plastic mismatches resulting from the TiC particles are efficiently canceled by matrix twinning, in contrast to metal matrix composites deforming by slip.« less
  • 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
  • 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
  • Many unusual thermomechanical properties of shape-memory alloys are directly connected with martensitic type phase transitions in these systems. Because the martensitic transformations, as a rule, are the first order transitions, a special attention should be given to a hysteretic behavior of shape-memory alloys. The most important characteristics of the temperature- or stress-induced martensitic transformation, have been previously studied in detail. It has been shown that such macroscopic state variables as inelastic strain or volume fraction of the martensite are always complex multi-valued functions of the temperature and external stress. Therefore, the shape-memory alloys should be considered as systems having anmore » infinite number of state equations, representing inelastic strain and volume fraction of martensite as functions of the external stress and temperature, correspondingly. Some of the phenomenological approaches for the thermomechanical state equations for shape memory alloys were recently published. In particular, a special type of differential equation describing evolution of the inelastic macroscopic strain and volume fraction of martensite as a function of the temperature has been proposed. Its application to partial temperature cycling processes in shape-memory alloys and some other problems associated with the irreversible processes caused by hysteresis are discussed in the present paper.« less