TEM observation of stress-induced martensite after nanoindentation of pseudoelastic Ti50Ni48Fe2

Zheng, Hongxing; Rao, Jiancun; Pfetzing, Janine; Frenzel, Jan; Somsen, Christoph; Eggeler, Gunther

doi:10.1016/j.scriptamat.2007.12.012

Cited by 23 publications

(6 citation statements)

References 15 publications

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“…the size of the indent during the experiment is larger than the remaining indent). This observation is in good accordance with data obtained for NiTiFe SMA, where transmission electron microscopy (TEM) results show the formation of stress-induced martensite in front of the indenter tip and the creation of a high dislocation density during nanoindentation [11]. The partial reversibility is associated with reversible martensitic transformations, while the accumulation of irreversible strain and the stabilization of stress-induced martensite are attributed to dislocations.…”

Section: Resultssupporting

confidence: 91%

“…The recovery of wires fatigued at 2 % strain is somewhere in between that of the asreceived and the solution annealed materials (RDR = 0.57). It is not surprising that the wires examined in this study have a remnant depth ratio larger than zero, because full pseudoelastic recovery is rarely reported in the literature for indentation studies [9,11]. Although nanoindentation was performed as close to the fracture surface as possible, no clear dependence of the nanohardness or RDR on the distance from the fracture surface of the fatigued wires is observed.…”

Section: Resultsmentioning

confidence: 81%

“…Dislocations may account for the stabilization of stress-induced martensite in some of the ultrafine grains within the microstructure, preventing their reverse transformation back to austenite upon unloading. Furthermore, it has already been shown that indenting a pseudoelastic, austenitic SMA can result in the formation of stress-induced martensite [11]. Based on previous results, it is known that the NiTiCr wires examined here contain a small volume fraction of titanium carbides [8].…”

Section: Resultsmentioning

confidence: 96%

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Influence of fatigue on the nanohardness of NiTiCr-wires

Frotscher

Young

Bei

et al. 2009

ESOMAT 2009 - 8th European Symposium on Martensitic Transformations

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Abstract.Testing parameters, such as rotational speed and bending radius, have a strong influence on the fatigue life of pseudoelastic NiTi shape-memory alloys during bending rotation fatigue (BRF) experiments [1,2]. Previous studies showed a decrease in the fatigue life for smaller bending radius (i.e. higher equivalent strain) and larger rotational speed. This observation is associated with an increase of dislocation density, the stabilization of stressinduced martensite during cycling, and an increase of the plateau stresses due to self-heating. In the present study, we examine the influence of these fatigue parameters on the nanohardness and shape recovery of pseudoelastic NiTiCr shape-memory alloy wires by nanoindentation. We show that nanoindentation is a suitable method for the characterization of fatigue-related microstructural changes, which affect the mechanical properties.

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 96%

See 1 more Smart Citation

Influence of fatigue on the nanohardness of NiTiCr-wires

Frotscher

Young

Bei

et al. 2009

ESOMAT 2009 - 8th European Symposium on Martensitic Transformations

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“…18 and 19 for an overview on the technique and its potential applications), which have been successfully applied to SMA both as thin films and bulk materials to characterize their thermomechanical properties and their evolution with thermal treatments. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] However, the multiaxial nature of deformation around the nanoindenter renders quantitative interpretation of the data very complex, especially for SMA which exhibit strong nonlinear behavior during thermal-or stress-induced transformation. This difficulty, together with interest in developing three-dimensional SMA devices for MEMS, has moved attention toward the use of nanocompression tests on simple features like micro and nanopillars produced by focused ion beam (FIB) milling.…”

Section: Introductionmentioning

confidence: 99%

Thermomechanical behavior at the nanoscale and size effects in shape memory alloys

2011

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Shape memory alloys (SMA) undergo reversible martensitic transformation in response to changes in temperature or applied stress, resulting in the properties of superelasticity and shape memory. At present, there is high scientific and technological interest to develop these properties at small scales and apply SMA as sensors and actuators in microelectromechanical system technologies. To study the thermomechanical properties of SMA at micro and nanoscales, instrumented nanoindentation is widely used to conduct nanopillar compression tests. By using this technique, superelasticity and shape memory at the nanoscale have been demonstrated in micro and nanopillars of Cu-Al-Ni SMA. However, the martensitic transformation seems to exhibit different behavior at small scales, and a size effect on superelasticity has been recently reported. In this study, we provide an overview of the thermomechanical properties of Cu-Al-Ni SMA at the nanoscale, with special emphasis on size effects. Finally, these size effects are discussed in light of the microscopic mechanisms controlling the martensitic transformation at the nanoscale.

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“…Such approaches, which involve careful transmission electron microscopy (TEM) observations of the deformed microstructures, have recently been applied to conventional, elasto-plastic materials [18,19]. In an earlier work [20], we performed a nanoindentation experiment with a sharp (Berkovich) indenter tip on a thin NiTiFe foil. Subsequent TEM observations of the indented region showed martensite stabilized by dislocations directly below the indent.…”

Section: Introductionmentioning

confidence: 99%

TEM investigation of the microstructural evolution during nanoindentation of NiTi

Pfetzing

Wagner

Simon

et al. 2009

ESOMAT 2009 - 8th European Symposium on Martensitic Transformations

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Abstract. The continuous measurement of loads and displacements during nanoindentation of shape memory alloys allows a detailed investigation of pseudoelasticity on the nano-scale. However, the resulting load-displacement data simultaneously reflect several elastic and inelastic deformation processes (i.e., stress-induced martensitic transformation, plastic deformation). In the present study, we perform microstructural investigations in order to analyze the complex interactions between these mechanisms in a Ni-rich alloy. The microstructures below indents from experiments with different maximum indentation loads are characterized post-mortem by transmission electron microscopy. For small maximum indentation loads, load-displacement data exhibit considerable pseudoelastic recovery, whereas higher indentation loads are associated with a more pronounced residual deformation after unloading. These differences are clearly related to microstructural changes below the indenter tip: While both stressinduced martensitic transformation and dislocation slip occur in general, higher maximum loads are associated with an increase in plastic deformation. The corresponding higher dislocation densities impede the reverse transformation to austenite. Stabilized martensite can be observed directly below the surface for high indentation loads. Our results show that nanoindentation of NiTi allows a systematic analysis of the interaction of plastic deformation and stress induced transformation into martensite.

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TEM observation of stress-induced martensite after nanoindentation of pseudoelastic Ti50Ni48Fe2

Cited by 23 publications

References 15 publications

Influence of fatigue on the nanohardness of NiTiCr-wires

Influence of fatigue on the nanohardness of NiTiCr-wires

Thermomechanical behavior at the nanoscale and size effects in shape memory alloys

TEM investigation of the microstructural evolution during nanoindentation of NiTi

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