Influence of cold work and heat treatment on the shape memory effect and plastic strain development of NiTi

Miller, David A.; Lagoudas, Dimitris C.

doi:10.1016/s0921-5093(00)01982-1

Cited by 185 publications

(91 citation statements)

References 20 publications

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“…31, it was observed that the two-stage transformation, corresponding to austenite → R-phase → martensite gives place to a one-stage transformation from austenite to martensite. Cold-worked NiTi subjected to annealing heat treatments may show two-step transformation [227,228]. This thermal behaviour may be completely destroyed by the welding procedure.…”

Section: Phase Transformation Temperaturesmentioning

confidence: 99%

Welding and Joining of NiTi Shape Memory Alloys: A Review

Oliveira

Miranda

Fernandes

2017

Progress in Materials Science

285

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Section: Phase Transformation Temperaturesmentioning

confidence: 99%

Welding and Joining of NiTi Shape Memory Alloys: A Review

Oliveira

Miranda

Fernandes

2017

Progress in Materials Science

285

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“…At stresses below this maximum, the transformation strain increased with stress, because the higher stresses were able to cause more of the martensite twin variants to reorient toward an orientation that favored the applied stress during cooling, therefore making more strain available to be recovered during the subsequent heating cycle during the transition to austenite. Eventually, at some level of stress, this reorientation effect is maximized, but further increases in stress become high enough to prevent full recovery of all the reoriented martensite, [30][31][32] and so the transformation strain level peaks and begins to decrease. Work output, being the mathematical product of the transformation strain and the applied stress, increased with applied stress for all of the stress levels reached (Figure 10), but would have eventually reached a maximum if even higher stress levels were attained, as our previous work on Ni 19.5-Ti 50.5 Pd 30 in compression has shown.…”

Section: B Stress-free Transformation Temperaturesmentioning

confidence: 99%

Characterization of Ternary NiTiPd High-Temperature Shape-Memory Alloys under Load-Biased Thermal Cycling

Bigelow

Padula

Garg

et al. 2010

Metall Mater Trans A

130

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While NiTiPd alloys have been extensively studied for proposed use in high-temperature shapememory applications, little is known about the shape-memory response of these materials under stress. Consequently, the isobaric thermal cyclic responses of five (Ni,Pd) 49.5 Ti 50.5 alloys with constant stoichiometry and Pd contents ranging from 15 to 46 at. pct were investigated. From these tests, transformation temperatures, transformation strain (which is proportional to work output), and unrecovered strain per cycle (a measure of dimensional instability) were determined as a function of stress for each alloy. It was found that increasing the Pd content over this range resulted in a linear increase in transformation temperature, as expected. At a given stress level, work output decreased while the amount of unrecovered strain produced during each load-biased thermal cycle increased with increasing Pd content, during the initial thermal cycles. However, continued thermal cycling at constant stress resulted in a saturation of the work output and nearly eliminated further unrecovered strain under certain conditions, resulting in stable behavior amenable to many actuator applications.

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“…Due to this, NiTi SMAs are frequently required to be "trained" before practical use in order to obtain a more stable and well known mechanical behavior [8][9][10]. This training process consists of carrying out thermal and/or mechanical cycling in the SMA in order to successively induce the formation of martensite and austenite, thus creating a dislocation pattern in the material and a preferable orientation path to the martensite variants [9,11]. As a consequence of training, there is an increase in the resistance of the material towards the formation of further dislocations, then more stable characteristics are achieved [12].…”

Section: Introductionmentioning

confidence: 99%

Influence of Strain Rate on the Functional Behavior of a Niti Alloy Under Pseudoelastic Training

Rodrigues¹,

Soares²,

Buono³

et al. 2017

Anais Do Congresso Anual Da ABM

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The present study deals with the effects of strain rate on the functional behavior of NiTi thin wires. The samples, in the austenitic condition at room temperature, were mechanically cycled 20 times by loading up to 6% strain followed by complete unloading, at 25°C. Four different quasi-static strain rates were assessed: 1x10 . The functional properties are described by means of critical stress to induce martensite, stress at maximum strain, energy dissipated per cycle and residual strain. The sensitivity of repeated cyclic deformation to strain rate is also analyzed in terms of phase stability. The results show that the fluctuation in the loading plateau, due to non-homogeneous transformation, increases with increasing strain rate. During cycling, it is observed that higher strain rates result in lower critical stress to induce martensite after the 5th cycle. However, the stress at maximum strain is higher at high strain rates, regardless the number of cycles. The accumulation of residual strain also increases with the strain rate due to the higher applied stress. During unloading, both the elastic deformation of stress-induced martensite and the reverse transformation seem to overlap at high strain rates. The dissipated energy behavior changes between the 1st and 20th cycle. No martensite is stabilized after training, but the intensity of the X-ray diffraction peaks of austenite increases with strain rate, as a result of stress relaxation.

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Influence of cold work and heat treatment on the shape memory effect and plastic strain development of NiTi

Cited by 185 publications

References 20 publications

Welding and Joining of NiTi Shape Memory Alloys: A Review

Welding and Joining of NiTi Shape Memory Alloys: A Review

Characterization of Ternary NiTiPd High-Temperature Shape-Memory Alloys under Load-Biased Thermal Cycling

Influence of Strain Rate on the Functional Behavior of a Niti Alloy Under Pseudoelastic Training

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