Site occupation of Nb atoms in ternary Ni–Ti–Nb shape memory alloys

Shi, Hui; Frenzel, Jan; Martinez, G.T.; Rompaey, Senne Van; Бакулин, А. В.; Kulkova, S. E.; Aert, Sandra Van; Schryvers, D.

doi:10.1016/j.actamat.2014.03.062

Cited by 47 publications

(20 citation statements)

References 43 publications

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“…The Nb-rich phase also contributes to the elastic strain field, strong stress redistribution and surrounding composition gradient49. According to refs 51 and 52, Nb element with a larger atomic radius substituting the Ti sublattice in NiTiNb specimen contributes to higher energy dissipation during transformation. This helps to increase hysteresis.…”

Section: Resultsmentioning

confidence: 99%

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

Wang

Zhang

Chen

et al. 2016

Sci Rep

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NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen.

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Section: Resultsmentioning

confidence: 99%

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

Wang

Zhang

Chen

et al. 2016

Sci Rep

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“…Although several investigations indicate that the response of the soft Nb-rich eutectic has the most pronounced effect on the transformation characteristics [33,34], also these smaller precipitates can play an important role. Not only do they reduce the Nb content of the matrix, thus affecting the transformation temperatures via the concentration dependence [35], but they also hamper the movement of the transformation front as seen in the captured image of an in situ TEM annealing sequence where the austenite-martensite interface is seen to be halted by rows of precipitates formed in a commercial (Ni-Ti)Nb 8.4 alloy extruded and quenched from 900°C (Fig. 7b) [36].…”

Section: Ni-ti-x Ternary Systemsmentioning

confidence: 97%

Advanced Electron Microscopy Characterisation of Important Precipitation and Ordering Phenomena in Shape Memory Systems

Schryvers

2015

Shap. Mem. Superelasticity

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The present paper discusses some important aspects of precipitation and ordering in alloy systems that show a martensitic transformation and can or are used as shape memory or superelastic metallic systems. The precipitates are investigated by a variety of conventional and advanced electron microscopy techniques, including atomic resolution, 3D slice-and-view, energy loss spectroscopy etc. Depending on the system, such secondary phases can decrease the probability of a displacive transformation by changing the phase stability in the system, such as in the case of Ni-Al or Ni-Ti-Pd, or can mechanically hinder the passage of the transformation interface, as in Ni-Ti-Nb. On the other hand, properly controlling the nucleation and growth of some precipitates can strongly improve the properties of some types of materials, as is the case for the well-known Ni 4 Ti 3 precipitates.

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“…Figure 2c shows the transverse-section in which fibers appear as speckles with spacing on the order of 100 nm. Figure 3a exposes the characteristic eutectic lamellar and globular mixture of Nb-rich b-phase and a-NiTiNb that is typical of dissolved Nb [3,5,9,12,18,21,[24][25][26][27][28][29][30][31]. The Nb-rich fibers in the deformation-processed material are aligned and discontinuous in Fig.…”

Section: Microstructure Characterizationmentioning

confidence: 97%

“…The b-Nb phase is presumably soft, and the critical stresses during isothermal pre-straining deformation are expected to plastically deform them, presuming that their flow stress matches that for pure Nb which is estimated between 150 and 200 MPa [1,2,23]. Plastic deformation of microconstituents as martensite deforms necessitates an increased thermal driving force for the reverse transformation that results in elevated A s and A f temperatures and the wide hysteresis [1,2,4,13,30], commonly referred to as a stabilization effect [4,10,[40][41][42].…”

Section: Introductionmentioning

confidence: 99%

Shape Memory Effect in Cast Versus Deformation-Processed NiTiNb Alloys

Hamilton

Lanba

Ozbulut

et al. 2015

Shap. Mem. Superelasticity

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The shape memory effect (SME) response of a deformation-processed NiTiNb shape memory alloy is benchmarked against the response of a cast alloy. The insoluble Nb element ternary addition is known to widen the hysteresis with respect to the binary NiTi alloy. Cast microstructures naturally consist of a cellular arrangement of characteristic eutectic microconstituents surrounding primary matrix regions. Deformation processing typically aligns the microconstituents such that the microstructure resembles discontinuous fiber-reinforced composites. Processed alloys are typically characterized for heat-to-recover applications and thus deformed at constant temperature and subsequently heated for SME recovery, and the critical stress levels are expected to facilitate plastic deformation of the microconstituents. The current work employs thermal cycling under constant bias stresses below those critical levels. This comparative study of cast versus deformation-processed NiTiNb alloys contrasts the straintemperature responses in terms of forward DT F = M s-M f and reverse DT R = A f-A s temperature intervals, the thermal hysteresis, and the recovery ratio. The results underscore that the deformation-processed microstructure inherently promotes irreversibility and differential forward and reverse transformation pathways.

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Site occupation of Nb atoms in ternary Ni–Ti–Nb shape memory alloys

Cited by 47 publications

References 43 publications

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

Advanced Electron Microscopy Characterisation of Important Precipitation and Ordering Phenomena in Shape Memory Systems

Shape Memory Effect in Cast Versus Deformation-Processed NiTiNb Alloys

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