Microstructural evolution and functional fatigue of a Ti–25Ta high-temperature shape memory alloy

Maier, Hans Jürgen; Karsten, E.; Paulsen, Alexander; Langenkämper, Dennis; Decker, Peer; Frenzel, Jan; Somsen, Christoph; Ludwig, Alfred; Eggeler, Gunther; Niendorf, Т.

doi:10.1557/jmr.2017.319

Cited by 12 publications

(11 citation statements)

References 31 publications

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“…7a and b, which look very different from what is typically observed for Ni-Ti SMAs, can only be appreciated when one considers the effect of the formation, dissolution and re-precipitation of x-phase [41,[43][44][45]. The smaller irregular peak 3 which follows represents the transformation from austenite to martensite, hampered by the formation of the x-phase which forms quickly [30,32,34]. From the experiment shown in Fig.…”

Section: Dsc Chartsmentioning

confidence: 89%

“…x-Phase Formation Materials research on the Ti-Ta system has shown that the formation of x-phase represents the main cause for functional degradation as it impedes the formation of martensite, e.g. [11,21,30,32]. The x-phase quickly forms at Fig.…”

Section: Discussion Spring Processing and Testingmentioning

confidence: 99%

“…8b. This has the drawback, however, that creep deformation results in irreversible plastic deformation and thus in a significant change of spring actuator geometry [32]. One may have the concern that an intermediate rejuvenation anneal can promote surface oxidation and thus affect structural fatigue.…”

Section: Discussion Spring Processing and Testingmentioning

confidence: 99%

“…Note that this temperature is significantly higher than the temperatures which are typically considered for the shape setting for Ni-Ti-based SMA spring actuators. It was chosen to avoid the formation of a-Ti and x-phase, which downgrade the functional performance of Ti-Ta HTSMAs [20][21][22][31][32][33][34].…”

Section: Thermo Mechanical Treatments and Wire Drawingmentioning

confidence: 99%

“…Atomistic calculations on the stability of phases, especially the x-phase, were performed [28][29][30]. Special emphasis was placed on the role of the x-phase during functional fatigue of Ti-Ta alloys [31][32][33][34] and it has been shown that by controlling the temperature during heating and cooling one can counteract fast functional degradation by x-phase precipitation. Functional fatigue was so far studied using uniaxial specimens.…”

Section: Introductionmentioning

confidence: 99%

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Laboratory-Scale Processing and Performance Assessment of Ti–Ta High-Temperature Shape Memory Spring Actuators

Paulsen

Dumlu

Piorunek

et al. 2021

Shap. Mem. Superelasticity

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Ti75Ta25 high-temperature shape memory alloys exhibit a number of features which make it difficult to use them as spring actuators. These include the high melting point of Ta (close to 3000 °C), the affinity of Ti to oxygen which leads to the formation of brittle α-case layers and the tendency to precipitate the ω-phase, which suppresses the martensitic transformation. The present work represents a case study which shows how one can overcome these issues and manufacture high quality Ti75Ta25 tensile spring actuators. The work focusses on processing (arc melting, arc welding, wire drawing, surface treatments and actuator spring geometry setting) and on cyclic actuator testing. It is shown how one can minimize the detrimental effect of ω-phase formation and ensure stable high-temperature actuation by fast heating and cooling and by intermediate rejuvenation anneals. The results are discussed on the basis of fundamental Ti–Ta metallurgy and in the light of Ni–Ti spring actuator performance.

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Section: Dsc Chartsmentioning

confidence: 89%

Section: Discussion Spring Processing and Testingmentioning

confidence: 99%

Section: Discussion Spring Processing and Testingmentioning

confidence: 99%

Section: Thermo Mechanical Treatments and Wire Drawingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Laboratory-Scale Processing and Performance Assessment of Ti–Ta High-Temperature Shape Memory Spring Actuators

Paulsen

Dumlu

Piorunek

et al. 2021

Shap. Mem. Superelasticity

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Electroplasticity Mechanisms in hcp Materials

et al. 2023

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Herein, the mechanisms of the electroplastic effect (EPE) in different hexagonal close‐packed (hcp) metals under varying loading conditions and current densities through the analysis of flow curves and microstructural changes are investigated. The investigations show a significant change in the forming behavior of the hcp materials as a result of superimposed electric current impulses. This behavior could be attributed to two effects. On the one hand, additional dislocation types are activated; on the other hand, new characteristic twin bands are formed. This is shown for all three hcp materials under investigation: Ti, Mg, and Zn. Furthermore, the hypothesis of the existence of a critical value of the current density at which a significant change in the plastic behavior occurs is verified by the experiments. The magnitude of this critical value for the analyzed hcp materials corresponds approximately to the theoretical values reported to be in the range of 1.6 to 2.0 kA mm−2. In addition to the current density, the duration of the pulses also has an influence on the EPE. Understanding the correlation between the individual activated deformation mechanisms during electric pulse treatment can be crucial for controlling the electroplastic forming processes in a systematic and targeted manner.

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A Kinetic Study on the Evolution of Martensitic Transformation Behavior and Microstructures in Ti–Ta High-Temperature Shape-Memory Alloys During Aging

Paulsen

Frenzel

Langenkämper

et al. 2018

Shap. Mem. Superelasticity

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Microstructural evolution and functional fatigue of a Ti–25Ta high-temperature shape memory alloy

Abstract: Abstract

Cited by 12 publications

References 31 publications

Laboratory-Scale Processing and Performance Assessment of Ti–Ta High-Temperature Shape Memory Spring Actuators

Laboratory-Scale Processing and Performance Assessment of Ti–Ta High-Temperature Shape Memory Spring Actuators

Electroplasticity Mechanisms in hcp Materials

A Kinetic Study on the Evolution of Martensitic Transformation Behavior and Microstructures in Ti–Ta High-Temperature Shape-Memory Alloys During Aging

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