Orientation-independent pseudoelasticity in small-scale NiTi compression pillars

Frick, Carl P.; Clark, Blythe; Orso, Steffen; Sonnweber-Ribic, Petra; Arzt, Eduard

doi:10.1016/j.scriptamat.2008.01.051

Cited by 54 publications

(51 citation statements)

References 26 publications

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“…Utilizing this simplified pillar geometry, researchers have extensively studied the size-dependent flow stress of single crystal micropillars using a flat-punch indenter as a compression testing machine [21][22][23][24]. The size effect has been investigated in numerous materials including Ni [25,26], Cu [27][28][29][30][31][32][33], Mo [34][35][36][37][38][39], NiTi shape memory alloy [40], Ni 3 Al [41], oxide dispersed alloy [42], Au [23,24,43,44], nanoporous Au [45,46], ceramics [47][48][49] and semiconductors [50][51][52][53]. However, the ease and flexibility with which micropillars can be produced provide further exciting possibilities for new studies aside from the size effect.…”

Section: Introductionmentioning

confidence: 99%

Novel methods for micromechanical examination of hydrogen and grain boundary effects on dislocations

Kheradmand

Dake

Barnoush

et al. 2012

Philosophical Magazine

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Most of what is known about the local interaction of dislocations with grain boundaries and hydrogen is based on transmission electron microscopy studies, which suffer from the distinct disadvantage that only extremely thin samples can be used. Recently, micropillar compression testing has become a popular means by which investigation of the size effect is conducted. This method, in combination with orientation imaging techniques, is used here to study the interaction of dislocations with a preselected grain boundary during the deformation of a bicrystalline specimen. Furthermore, by utilizing a custom built electrochemical cell, the micropillar compression testing can be extended to study in situ examination of micropillars charged with hydrogen. The effects of hydrogen and grain boundary on the deformation process in this small, but still bulk-like volume are presented, and our initial results reveal the value of this new technique for investigations of hydrogen embrittlement and grain boundary strengthening.

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Section: Introductionmentioning

confidence: 99%

Novel methods for micromechanical examination of hydrogen and grain boundary effects on dislocations

Kheradmand

Dake

Barnoush

et al. 2012

Philosophical Magazine

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“…The fixed-thickness TiO 2 layer is supposed to dominate in the small pillars, while it has been observed that pillars with diameter smaller than 200 nm exhibit less strainhardening than pillars with larger diameters, and the 162 nm [210] oriented pillar even shows a perfect plateau [14].…”

Section: Ti Oxide -Plasticitymentioning

confidence: 99%

“…At T = 298 K, a stress value 800 MPa has been reported as the point in which the forward martensitic phase transformation initiates [14,33]. Y = 4.…”

Section: Model Parametersmentioning

confidence: 99%

“…The following boundary conditions are adopted to simulate the pillar compression tests: u i = 0 at x i = 0 for i = 1, 2, 3, and u 3 =û 3 at x 3 = h. In [14], the experimental stress-strain curves have shown that the strainhardening rate during the phase transformation is highest for medium-size pillars with diameter between 200 and 400 nm, and the differences in the strain-hardening rate are attributed to the taper shape of the individual pillar. However, this explanation has not been further quantified.…”

Section: Finite Element Simulationsmentioning

confidence: 99%

“…In addition, compression tests on single crystal Ti-50.9 at.%Ni pillars have shown that the strain recovery diminishes with the pillar diameter and is suppressed for pillars with diameter smaller than about 200 nm [13]. Further study has revealed that this trend of losing superelasticity at small pillar sizes does not depend on the crystal orientations [14]. Different explanations of this size-dependent behavior have been proposed.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the role of Ti oxide layer in the size-dependent superelasticity of NiTi pillars: Modeling and simulation

Qiao

Radovitzky

2013

Acta Materialia

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Recent compression tests of NiTi pillars of a wide range of diameters have shown significant size dependency in the strain recovered upon unloading. In this paper, we propose a numerical model supporting the previously proposed explanation that the external Ti oxide layer may be responsible for the loss of superelasticity in the small pillars. The shape memory alloy at the center of the pillar is described using a nonlocal superelastic model, whereas the Ti oxide layer is modeled as elastoplastic. Voigt-average analysis and finite element calculations of the tests are compared to experiments for the range of pillar sizes considered in the experiments. The simulation results also suggest a size-dependent strain hardening due to the constraint on the phase transformation effected by the confining Ti oxide layer.

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Size Independent Shape Memory Behavior of Nickel–Titanium

et al. 2010

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Shape memory alloys represent a class of so-called ''smart'' materials that can be returned to their original shape after deformation, either spontaneously or through the application of heat. While several alloys are capable of shape memory behavior, nickel-titanium (NiTi) is the most extensively researched due primarily to its relatively large deformation recoverability, [1] as well as its high strength, [2] corrosion resistance, [3] biocompatibility, [4] and high intrinsic damping. [5] The shape memory effect for NiTi results from a reversible martensitic phase transformation, in which the crystal structure shifts from a B2 (austenite) to a B19 0 (martensite) phase in a shear-like manner. Depending upon composition and processing history, the stress-induced martensitic phase transformation is capable of two responses: pseudoelasticity and shape memory behavior. Pseudoelasticity occurs when the martensite is unstable at the testing temperature and spontaneously reverts back to austenite upon unloading, recovering the previously accumulated deformation. Shape memory behavior occurs when the martensite is stable at the testing temperature, requiring heat to revert to austenite and recover the strain associated with the phase transformation.Monotonic uniaxial stress-strain testing of shape memory NiTi is well-known to exhibit four stages of deformation, each dominated by a specific mechanism as a function of increasing strain: (I) elastic deformation of austenite, (II) austeniteto-martensite phase transformation, (III) elastic deformation of martensite, and (IV) martensite plasticity. [6] The martensite phase transformation is exemplified by a critical stress at which the phase transformation initiates, followed by a decrease in stress/strain slope signifying the propagation of the martensite throughout the sample. [1] Nominal values of the critical martensite initiation stress, transformation slope, and transformation strain are heavily influenced by processing history, microstructure, and crystallographic orientation. Because the phase transformation is temperature dependent, COMMUNICATION[*] Dr.While shape memory alloys such as NiTi have strong potential as active materials in many small-scale applications, much is still unknown about their shape memory and deformation behavior as size scale is reduced. This paper reports on two sets of experiments which shed light onto an inconsistent body of research regarding the behavior of NiTi at the nano-to microscale. In situ SEM pillar bending experiments directly show that the shape memory behavior of NiTi is still present for pillar diameters as small as 200 nm. Uniaxial pillar compression experiments demonstrate that plasticity of the phase transformation in NiTi is size independent and, in contrast to bulk single crystal observations, is not influenced by heat treatment (i.e., precipitate structure).808

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Orientation-independent pseudoelasticity in small-scale NiTi compression pillars

Cited by 54 publications

References 26 publications

Novel methods for micromechanical examination of hydrogen and grain boundary effects on dislocations

Novel methods for micromechanical examination of hydrogen and grain boundary effects on dislocations

Investigation of the role of Ti oxide layer in the size-dependent superelasticity of NiTi pillars: Modeling and simulation

Size Independent Shape Memory Behavior of Nickel–Titanium

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