scholarly journals Coherent Precipitates as a Condition for Ultra-Low Fatigue in Cu-Rich Ti53.7Ni24.7Cu21.6 Shape Memory Alloys

2021 ◽  
Author(s):  
L. Bumke ◽  
N. Wolff ◽  
C. Chluba ◽  
T. Dankwort ◽  
L. Kienle ◽  
...  
Keyword(s):  
Grain Size ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Internal Stresses ◽  
Cyclic Stability ◽  
Partial Loss ◽  
Functional Fatigue ◽  
Transformation Temperatures ◽  
Different Temperatures ◽  
B2 Phase

AbstractSputtered Ti–rich TiNiCu alloys are known to show excellent cyclic stability. Reversibility is mostly influenced by grain size, crystallographic compatibility and precipitates. Isolating their impact on cyclic stability is difficult. Ti2Cu precipitates for instance are believed to enhance reversibility by showing a dual epitaxy with the B2 and B19 lattice. Their influence on the functional fatigue, if they partly lose the coherency is still unknown. In this study, sputtered Ti53.7Ni24.7Cu21.6 films have been annealed at different temperatures leading to a similar compatibility (λ2 ~ 0.99), grain size and thermal cyclic stability. Films annealed at 550 °C exhibit a superior superelastic fatigue resistance but with reduced transformation temperatures and enthalpies. TEM investigations suggest the formation of Guinier–Preston (GP) zone-like plate precipitates and point towards a coherency relation of the B2 phase and finely distributed Ti2Cu precipitates (~ 60 nm). Films annealed at 700 °C result in the growth of Ti2Cu precipitates (~ 280 nm) with an irregular distribution and a partial loss of their coherency. Thus, GP zones are assumed to cause the reduction of transformation temperatures and enthalpies due to increased internal stresses, whereas the coherency relation of both, Ti2Cu and GP zones, help to increase the superelastic stability, well beyond 107 cycles.

Modeling of Internal Damage Evolution During Actuation Fatigue in Shape Memory Alloys

2018 ◽  
Author(s):  
Francis R. Phillips ◽  
Daniel Martin ◽  
Dimitris C. Lagoudas ◽  
Robert W. Wheeler
Keyword(s):  
Phase Transformation ◽  
Constitutive Model ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Damage Evolution ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Internal Damage ◽  
Functional Fatigue ◽  
Non Linear

Shape memory alloys (SMAs) are unique materials capable of undergoing a thermo-mechanically induced, reversible, crystallographic phase transformation. As SMAs are utilized across a variety of applications, it is necessary to understand the internal changes that occur throughout the lifetime of SMA components. One of the key limitations to the lifetime of a SMA component is the response of SMAs to fatigue. SMAs are subject to two kinds of fatigue, namely structural fatigue due to cyclic mechanical loading which is similar to high cycle fatigue, and functional fatigue due to cyclic phase transformation which typical is limited to the low cycle fatigue regime. In cases where functional fatigue is due to thermally induced phase transformation in contrast to being mechanically induced, this form of fatigue can be further defined as actuation fatigue. Utilizing X-ray computed microtomography, it is shown that during actuation fatigue, internal damage such as cracks or voids, evolves in a non-linear manner. A function is generated to capture this non-linear internal damage evolution and introduced into a SMA constitutive model. Finally, it is shown how the modified SMA constitutive model responds and the ability of the model to predict actuation fatigue lifetime is demonstrated.

scholarly journals Effect of Ni-Content on the Transformation Temperatures in NiTi-20 at. % Zr High Temperature Shape Memory Alloys

Metals ◽  
2017 ◽  
Vol 7 (11) ◽  
pp. 511 ◽  
Author(s):  
Matthew Carl ◽  
Jesse Smith ◽  
Brian Van Doren ◽  
Marcus Young
Keyword(s):  
High Temperature ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Transformation Temperatures ◽  
Ni Content

Orientation relationship between TiC carbides and B2 phase in as-cast and heat-treated NiTi shape memory alloys

2006 ◽  
Vol 438-440 ◽  
pp. 879-882 ◽  
Author(s):  
Zhonghua Zhang ◽  
Jan Frenzel ◽  
Christoph Somsen ◽  
Josef Pesicka ◽  
Klaus Neuking ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Orientation Relationship ◽  
Heat Treated ◽  
B2 Phase ◽  
Niti Shape Memory Alloys

Effect of Nitrogen Addition on TiNi Shape Memory Alloys

2020 ◽  
Vol 12 (9) ◽  
pp. 1403-1408
Author(s):  
Izaz Ur Rehman ◽  
Tae-Hyun Nam
Keyword(s):  
Mechanical Properties ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Tensile Tests ◽  
Nitrogen Addition ◽  
Ternary Alloys ◽  
X Ray Diffraction ◽  
Transformation Temperatures ◽  
Arc Melting ◽  
Type Phase

In present paper we will show how nitrogen effects microstructures, transformation temperatures, and mechanical properties of equiatomic Ti50–Ni50 and Ti-rich Ti51–Ni49 binary shape memory alloys. 0.5 at.% of nitrogen was added to prepare Ti50–Ni49.5–N0.5, and Ti51–Ni48.5–N0.5 (at.%) alloys by arc-melting. Microstructures were investigated by scanning electron microscope (SEM), phase constitutions were investigated by X-ray diffraction (XRD), transformation temperatures were investigated by differential scanning calorimeter (DSC) and mechanical properties were tested by tensile tests. Solutions treated Ti–Ni–N shape memory alloys contain TiNi matrix without nitrogen, Ti2Ni type phase containing a small amount of nitrogen and a new Ti2N type phase containing a small amount of nickel. Compared with Ti50–Ni50 and Ti51–Ni49 binary alloys, the martensitic transformation starts temperatures (Ms) of Ti50–Ni49.5–N0.5 and Ti51–Ni48.5–N0.5 ternary alloys decreased from 63.4 °C to 41.6 °C and from 85.3 °C to 79.4 °C, respectively. By adding N, fracture strain decreased and incomplete superelasticity was observed.

scholarly journals Effect of Nitrogen on Transformation Temperatures of Arc-Melted Ti-Ni Shape Memory Alloys.

1999 ◽  
Vol 17 (1) ◽  
pp. 78-85
Author(s):  
Yoshihiro SATO ◽  
Hidenori TAKAHASHI ◽  
Hiroyuki KOKAWA ◽  
Takeshi KUWANA ◽  
Kiyoshi YAMAUCHI ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Transformation Temperatures
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