Abrupt Softening Phenomenon in a Shape Memory CuAlNi Single Crystal under Uniaxial Compression

2009 ◽  
Vol 614 ◽  
pp. 181-185 ◽  
Author(s):  
Li Sun ◽  
W.M. Huang
Keyword(s):  
Phase Transformation ◽  
Martensitic Transformation ◽  
Single Crystal ◽  
Shape Memory ◽  
Uniaxial Compression ◽  
Anomalous Behavior ◽  
Good Evidence ◽  
The Other ◽  
Martensite Variant ◽  
Transformation Front

Abrupt softening phenomenon was observed in a shape memory CuAlNi single crystal upon uniaxial compression. Sudden martensite variant(s) reorientation was found to be the reason behind this anomalous behavior. The significance of this finding is twofold. On one hand, it clearly demonstrates that the stress induced transformation can follow a sequence of the phase transformation (martensitic transformation, austenite to martensite) and then reorientation (from one martensite variant to another). On the other hand, the anomalous softening provides a good evidence for explaining the propagation of the phase transformation front.

scholarly journals Microstructure and Phase Transformation Analysis of Ni50−xTi50Lax Shape Memory Alloys

Crystals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 345 ◽  
Author(s):  
Weiya Li ◽  
Chunwang Zhao
Keyword(s):  
Phase Transformation ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensite Transformation ◽  
Transformation Behavior ◽  
Ni Content ◽  
Start Temperature

The microstructure and martensitic transformation behavior of Ni50−xTi50Lax (x = 0.1, 0.3, 0.5, 0.7) shape memory alloys were investigated experimentally. Results show that the microstructure of Ni50−xTi50Lax alloys consists of a near-equiatomic TiNi matrix, LaNi precipitates, and Ti2Ni precipitates. With increasing La content, the amounts of LaNi and Ti2Ni precipitates demonstrate an increasing tendency. The martensitic transformation start temperature increases gradually with increasing La content. The Ni content is mainly responsible for the change in martensite transformation behavior in Ni50−xTi50Lax alloys.

Influence of Rare Earth on Shape Memory and Martensitic Transformation Behaviors of a FeMnSiCr Alloy

2005 ◽  
Vol 475-479 ◽  
pp. 1995-1998
Author(s):  
Xing Huang ◽  
Shipu Chen ◽  
T.Y. Hsu
Keyword(s):  
Rare Earth ◽  
Martensitic Transformation ◽  
Shape Memory ◽  
Stacking Faults ◽  
The Other ◽  
Strengthening Effect ◽  
Shape Memory Property ◽  
Solid Solution Strengthening ◽  
Solution Strengthening ◽  
Shockley Dislocation

Proper amount of blend rare earth (RE), e.g. less than 0.2 wt%, was added into a Fe25Mn6Si5Cr alloy and showed beneficial effect on its shape memory property. On the other hand, measurements of internal friction revealed that RE-addition reduces the Ms temperature and the amount of thermal-induced martensite. Higher La-content in thin hcp (e) plates than that in fcc (g) matrix was observed by analytical TEM. Thermodynamic calculations also indicated a relatively high equilibrated concentration in e and a strong interaction between La atom and 1/6<112> Shockley dislocation. Except for the grain refinement and solid-solution strengthening effect, the influence of RE on the g ® e martensitic transformation is discussed in taking into account both the Suzuki Effect and Suzuki Lock. The former results in a reduced stacking fault energy, while the Suzuki Lock hinders the movement of Shockley partials and thus the extension of stacking faults.

In situ TEM study of irradiation-induced transformation in TiNi shape memory alloys

2003 ◽  
Vol 792 ◽  
Author(s):  
X. T. Zu ◽  
F.R. Wan ◽  
S. Zhu ◽  
L. M. Wang
Keyword(s):  
Phase Transformation ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Electron Irradiation ◽  
Room Temperature ◽  
Critical Voltage ◽  
In Situ Tem ◽  
In Situ Observation

ABSTRACTTiNi shape memory alloy (SMA) has potential applications for nuclear reactors and its phase stability under irradiation is becoming an important topic. Some irradiation-induced diffusion-dependent phase transformations, such as amorphization, have been reported before. In the present work, the behavior of diffusion-independent phase transformation in TiNi SMA was studied by electron irradiation at room temperature. The effect of irradiation on the martensitic transformation of TiNi shape memory alloys was studied by Transmission Electron Microscopy (TEM) with in-situ observation and differential scanning calorimeter (DSC). The results of TEM and DSC measurements show that the microstructure of samples is R phase at room temperature. Electron irradiations were carried out using several different TEM with accelerating voltage of 200 kV, 300 kV, 400 kV and 1000 kV. Also the accelerating voltage in the same TEM was changed to investigate the critical voltage for the effect of irradiation on phase transformation. It was found that a phase transformation occurred under electron irradiation above 320 kV, but never appeared at 300 kV or lower accelerating voltage. Such phase transformation took place in a few seconds of irradiation and was independent of atom diffusion. The mechanism of Electron-irradiation-induced the martensitic transformation due to displacements of atoms from their lattice sites produced by the accelerated electrons.

Phase Transformation and Microstructures in Ni and Cu Base Ferromagnetic Shape Memory Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 3157-3162 ◽  
Author(s):  
Takuro Kushima ◽  
Koichi Tsuchiya ◽  
Yasuyoshi Sho ◽  
Takafumi Yamada ◽  
Yoshikazu Todaka ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Magnetic Property ◽  
Chemical Composition ◽  
Martensitic Transformation ◽  
Curie Temperature ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Ferromagnetic Shape Memory Alloys ◽  
Ferromagnetic Shape Memory

Effect of chemical composition was investigated on martensitic transformation temperatures, Curie temperature, magnetization and microstructures for Ni-(Mn, Fe, Co)-Ga and Cu-Mn-Ga systems. In the Ni-(Mn, Fe, Co)-Ga alloys, which is a modification of Ni-Mn-Ga systems, the Af and TC over 400 K were achieved. Cu-Mn-Ga alloy exhibited shape memory effect at temperatures above 373 K and had TC over 400 K. Furthermore, Cu-Mn-Ga exhibits good ductility even in polycrystalline condition unlike the case of Ni-Mn-Ga. Effect of addition of the fourth element to improve the magnetic property is under investigation.

Phase Transformation in Ti-Ni-Ta Shape Memory Alloy

2007 ◽  
Vol 130 ◽  
pp. 147-150 ◽  
Author(s):  
Zdzisław Lekston ◽  
Tomasz Goryczka
Keyword(s):  
Phase Transformation ◽  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Medical Application ◽  
Precipitation Process ◽  
X Ray Diffraction ◽  
Martensitic Transformation Temperature ◽  
X Ray ◽  
Solution Treated

A new Ti50Ni48.7Ta1.3 shape memory alloy was designed for medical application. In order to influence the martensitic transformation temperature the alloy was solution treated and additionally aged at 400oC for various time. Phase transformation was studied applying differential scanning calorimeter (DSC) and X-ray diffraction techniques. The ageing causes that the martensitic transformation occurs in two steps: B2↔R↔B19’ during cooling and heating. During cooling the transformations: B2→R and R→B19’ are well separated whereas on heating they are overlapped. Also ageing causes a shift of temperatures of the martensitic transformation into the higher region. It is due to the precipitation process. Precipitates of the Ni4Ti3 phase were observed. Applied thermal treatment leads to shift of the transformation temperatures below temperature of a human body. This makes the Ti-Ni-Ta alloy attractive for application in medicine.

Thermomechanical effects on phase transformations in single-crystal Cu–Al–Ni shape-memory alloy

2007 ◽  
Vol 22 (4) ◽  
pp. 994-1003 ◽  
Author(s):  
H.-S. Zhang ◽  
K. Komvopoulos
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Single Crystal ◽  
Shape Memory ◽  
Elevated Temperatures ◽  
Czochralski Method ◽  
Tensile Tests ◽  
Transformation Temperatures ◽  
Experimental Findings ◽  
Cyclic Straining

Single-crystal rods of Cu–Al–Ni shape-memory alloy fabricated from a molten pool of 82 wt% Cu, 14 wt% Al, and 4 wt% Ni by the Czochralski method were first heated to ∼870 °C and then quenched to obtain austenitic microstructures. Various microanalysis techniques were used to determine the chemical composition, microstructure, and phase-transformation temperatures of the produced alloy. Cyclic tensile tests with in situ temperature control demonstrated the occurrence of pseudoelastic deformation at elevated and close to phase-transformation temperatures and provided insight into the temperature dependence of the phase-transformation stress, damping characteristics, and cyclic straining of single-crystal Cu–Al–Ni alloy. The stress hysteresis observed in the pseudoelastic deformation cycles decreased at elevated temperatures. The stress response at different temperatures is associated with the formation, growth, and coalescence of martensite variants. Stress-induced phase-transformation mechanisms, coalescence of twin variants, and energy dissipation by pseudoelastic deformation are discussed in the context of experimental findings. The results illustrate the potential of single-crystal Cu–Al–Ni as a structural material for dynamic microsystems and temperature sensors.

Evolutions of Microstructure and Phase Transformation in Cu-Al-Fe-Nb/Ta High-Temperature Shape Memory Alloys

2015 ◽  
Vol 833 ◽  
pp. 67-70
Author(s):  
Shui Yuan Yang ◽  
Cui Ping Wang ◽  
Yu Su ◽  
Xing Jun Liu
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Transformation Behavior ◽  
Two Phase ◽  
Phase Transformation Behavior ◽  
Three Phase

The evolutions of microstructure and phase transformation behavior of Cu-Al-Fe-Nb/Ta high-temperature shape memory alloys under the quenched and aged states were investigated in this study, including Cu-10wt.% Al-6wt.% Fe, Cu-10wt.% Al-4wt.% Fe-2wt.% Nb and Cu-10wt.% Al-4wt.% Fe-2wt.% Ta three types alloys. The obtained results show that after quenching, Cu-10wt.% Al-6wt.% Fe alloy exhibits two-phase microstructure of β′1 martensite + Fe (Al,Cu) phase; Cu-10wt.% Al-4wt.% Fe-2wt.% Nb alloy also has two-phase microstructure of (β′1 + γ′1 martensites) + Nb (Fe,Al,Cu)2 phase; Cu-10wt.% Al-4wt.% Fe-2wt.% Ta alloy is consisted of three-phase of (β′1 + γ′1 martensites) + Fe (Al,Cu,Ta) + Ta2(Al,Cu,Fe)3 phases. However, α (Cu) phase precipitates after aging for three alloys; and Fe (Al,Cu,Nb) phase is also present in Cu-10wt.% Al-4wt.% Fe-2wt.% Nb alloy. All the studied alloys exhibit complicated martensitic transformation behaviors resulted from the existence of two types martensites (β′1 and γ′1).

Effect of L21 Ordering on the Martensitic and Intermartensitic Transformations in a Ni-Mn-Ga Shape Memory Alloy

2007 ◽  
Vol 130 ◽  
pp. 127-134
Author(s):  
Concepcio Seguí ◽  
Jaume Pons ◽  
Eduard Cesari
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Single Crystal ◽  
Shape Memory ◽  
Parent Phase ◽  
Heat Treatments ◽  
Free Energies ◽  
Transformation Temperatures ◽  
Reverse Martensitic Transformation ◽  
Order Degree

The present work analyses the influence of austenite ordering on a single crystal Ni-Mn- Ga alloy which displays, on cooling, a sequence of martensitic (MT) and intermartensitic (IMT) transformations. The MT and IMT show distinct behaviour after ageing in austenite: while the MT temperatures are not affected by the performed heat treatments, the IMT shifts toward lower temperatures after quenching from increasing temperatures, progressive recovery occurring upon ageing in parent phase. Such evolution can be related to changes in the L21 order degree, in the sense that ordering favours the occurrence of the intermartensitic transformation, while it does not affect noticeably the forward and reverse martensitic transformation temperatures. The closeness of the free energies of the different martensite structures allows to explain this behaviour.

TWO-WAY SHAPE MEMORY EFFICIENCY OF THE Ti-Ni 54.4 Wt. (%) ENHANCED BY THERMAL TREATMENTS

2013 ◽  
Vol 06 (06) ◽  
pp. 1350057 ◽  
Author(s):  
CRISTINA URBINA ◽  
SILVIA DE LA FLOR ◽  
FRANCESC GISPERT ◽  
FRANCESC FERRANDO
Keyword(s):  
Phase Transformation ◽  
Thermal Cycling ◽  
Shape Memory ◽  
The Other ◽  
Thermal Treatments ◽  
Transformation Behavior ◽  
Memory Efficiency ◽  
Heat Treated ◽  
Sample Set ◽  
Training Efficiency

This paper experimentally analyzes the influence of repeated thermal cycling at zero stress on the two-way training efficiency for developing the two-way shape memory effect in TiNi shape memory alloys. Four different sets of TiNi wire are used in the study: two sets have been heat-treated to ensure a transformation path with no R-phase, whereas the other two sets have had the same heat-treatment which is then followed by repeated thermal cycling at zero stress to stabilize their phase transformation behavior. Subsequently, thermal cycling under constant stress two-way training is performed on each sample set. The study then analyzes the training efficiency and the recoverable two-way memory strain for each sample set. The results suggest that to obtain the best two-way material performance, that is, to obtain a substantial two way memory strain together with an increase in the efficiency of the training, the TiNi wire should be thermally cycled at zero stress prior to training until the phase transformation is stabilized.

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