Influence of carbon on martensitic phase transformations in NiTi shape memory alloys

Frenzel, Jan; Zhang, Z.; Somsen, Christoph; Neuking, K.; Eggeler, G.

doi:10.1016/j.actamat.2006.10.006

Cited by 145 publications

(87 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…It was not possible to clearly rationalize each single diffraction peak, due to the fact that XRD experiments were performed on slightly oxidized wires where additional surface phases contribute to the diffracted intensities. The undeformed wire mainly consist of B19 0 , only small volume fractions of B2, R phase, and TiC (common impurity in VIM-melted NiTi [67]) are present. After wire drawing, the peak intensities change and peak widths slightly increase.…”

Section: Resultsmentioning

confidence: 99%

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Birk

Biswas

Frenzel

et al. 2016

Shap. Mem. Superelasticity

View full text Add to dashboard Cite

Pseudoelasticity (PE) in shape memory alloys relies on the formation of stress-induced martensite during loading and on the reverse transformation during unloading. PE yields reversible strains of up to 8 % and is applied in applications such as medical implants, flexible eye glass frames, damping elements, and others. Unfortunately, PE shows a strong temperature dependence and thus can only be exploited within a relatively narrow temperature window. The present work focuses on a related process, which we refer to as twinning-induced elasticity (TIE). It involves the growth and shrinkage of martensite variants which are stabilized by dislocations, which are introduced by appropriate cold work. TIE yields reversible strains of the order of 3 %. The TIE effect does not suffer from the strong temperature dependence of PE. The weak temperature dependence of mechanical TIE properties makes TIE attractive for applications where temperature fluctuations are large. In the present work, we study the TIE effect focusing on Ni 50 Ti 50 shape memory alloy wires. The degree of plastic pre-deformation of the initial material represents a key parameter of the ingot metallurgy processing route. It governs the exploitable recoverable strain, the apparent Young's modulus, and the widths of the mechanical hysteresis. Dynamic mechanical analysis is used to study the effects of pre-deformation on elementary microstructural processes which govern TIE.

show abstract

Section: Resultsmentioning

confidence: 99%

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Birk

Biswas

Frenzel

et al. 2016

Shap. Mem. Superelasticity

View full text Add to dashboard Cite

show abstract

“…First, oxygen and carbon [11] pick-up are known to affect the transformation criteria with powder metallurgy parts containing 1500-3000 ppm oxygen levels [12]. Oxygen and carbon pick-up have been shown to increase linearly in relation to energy density of lasermelted NiTi [13].…”

Section: Introductionmentioning

confidence: 99%

On the Transformation Behavior of NiTi Shape-Memory Alloy Produced by SLM

Speirs

Wang

Baelen

et al. 2016

Shap. Mem. Superelasticity

113

View full text Add to dashboard Cite

Selective laser melting has been applied as a production technique of nickel titanium (NiTi) parts. In this study, the scanning parameters and atmosphere control used during production were varied to assess the effects on the final component transformation criteria. Two production runs were completed: one in a high (*1800 ppm O 2 ) and one in a low-oxygen (*220 ppm O 2 ) environment. Further solution treatment was applied to analyze precipitation effects. It was found that the transformation temperature varies greatly even at identical energy densities highlighting the need for further in-depth investigations. In this respect, it was observed that oxidation was the dominating factor, increased with higher laser power adapted to higher scanning velocity. Once the atmospheric oxygen content was lowered from 1800 to about 220 ppm, a much smaller variation of transformation temperatures was obtained. In addition to oxidation, other contributing factors, such as nickel depletion (via evaporation during processing) as well as thermal stresses and textures, are further discussed and/or postulated. These results demonstrated the importance of processing and material conditions such as O 2 content, powder composition, and laser scanning parameters. These parameters should be precisely controlled to reach desired transformation criteria for functional components made by SLM.

show abstract

“…The graphite crucible is used because of its excellent chemical homogeneity. However, it is known that NiTi melts dissolve carbon from the crucible during solidification and hence can alter the transformation behavior [61]. Several studies aiming to minimize this issue have been reported.…”

Section: Bulk Micromachined Smamentioning

confidence: 99%

Micromachined Shape-Memory-Alloy Microactuators and Their Application in Biomedical Devices

2015

View full text Add to dashboard Cite

Shape memory alloys (SMAs) are a class of smart materials characterized by shape memory effect and pseudo-elastic behavior. They have the capability to retain their original form when subjected to certain stimuli, such as heat or a magnetic field. These unique properties have attracted many researchers to seek their application in various fields including transportation, aerospace, and biomedical. The ease process adaption from semiconductor manufacturing technology provides many opportunities for designing micro-scale devices using this material. This paper gives an overview of the fabrication and manufacturing technique of thin-film and bulk micromachined SMAs. Key features such as material properties, transformation temperature, material composition, and actuation method are also presented. The application and micromechanism for both thin-film and bulk SMA are described. Finally, the microactuator devices emphasized for biomedical applications such as microgrippers and micropumps are highlighted. The presented review will provide information for researchers who are actively working on the development of SMA-based microscale biomedical devices.

show abstract

Influence of carbon on martensitic phase transformations in NiTi shape memory alloys

Cited by 145 publications

References 0 publications

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

On the Transformation Behavior of NiTi Shape-Memory Alloy Produced by SLM

Micromachined Shape-Memory-Alloy Microactuators and Their Application in Biomedical Devices

Contact Info

Product

Resources

About