Shape Memory Characteristics of NiTi Alloy Wire under Various Constrained Stresses

2012 ◽  
Vol 567 ◽  
pp. 135-140 ◽  
Author(s):  
Yan Feng Li ◽  
X.J. Mi ◽  
Xiang Qian Yin ◽  
H.F. Xie
Keyword(s):  
Shape Memory ◽  
Annealing Temperature ◽  
Volume Fraction ◽  
Niti Alloy ◽  
Transformation Temperatures ◽  
Austenitic Transformation ◽  
Heating And Cooling ◽  
Recovery Strain ◽  
High Annealing ◽  
Memory Characteristics

The present research aims to understand the transformation temperatures and recovery strain of NiTi wires during heating and cooling under various constrained stresses. Both constrained stress and annealing temperature have significant effects on the shape memory characteristics. In general, increasing constrained stress causes an increase of the austenitic and martensitic transformation temperatures and a decrease of the recovery strain. This effect can be attributed to that the constrained stress inhibits the austenitic transformation, and thus more volume fraction of the martensite is retained during heating. The high annealing temperature leads to the decrease in the recovery strain.

THE INCREASE OF THE MARTENSITIC DEFORMATION DURING SHAPE MEMORY EFFECT IN DEFORMED TiNi

2012 ◽  
Vol 05 (01) ◽  
pp. 1250011 ◽  
Author(s):  
GEORGIY FIRSTOV ◽  
YURI KOVAL ◽  
ALEKSANDR LOTKOV ◽  
VICTOR GRISHKOV ◽  
JAN VAN HUMBEECK
Keyword(s):  
Thermal Treatment ◽  
Shape Memory ◽  
Volume Fraction ◽  
Niti Alloy ◽  
Structure Refinement ◽  
External Stress ◽  
Low Temperature Annealing ◽  
Ultrafine Structure ◽  
Hot Rolled ◽  
Memory Characteristics

The evolution of the ultrafine structure, obtained at thermal treatment below recrystallization, and its effect onto shape memory characteristics in NiTi alloy was under study. It was shown that low temperature annealing (< 0.5 Tmelt) of the hot rolled NiTi leads to the structure refinement accompanied by the growth in accumulated martensite deformation. It was suggested that this is possible due to the increase of the volume fraction of martensite crystals properly oriented in respect to external stress.

Transformation Temperatures, Shape Memory and Magnetic Properties of Hafnium Modified Ti-Ta Based High Temperature Shape Memory Alloys

2017 ◽  
Vol 36 (2) ◽  
pp. 113-119
Author(s):  
W.Q. Khan ◽  
Q. Wang ◽  
X. Jin
Keyword(s):  
High Temperature ◽  
Shape Memory ◽  
Alloy System ◽  
Heat Of Reaction ◽  
Transformation Temperatures ◽  
Dsc Measurements ◽  
Recovery Strain ◽  
Shape Memory Properties ◽  
Three Point Bend Test ◽  
Point Bend

AbstractIn this study the modification effect of Hf content on the shape memory properties and magnetic permeability of a 75.5-77Ti-20Ta-3-4.5Hf alloy system has been systematically studied by DSC, three-point bend test, vector network analyzer and XRD. The martensitic transformation temperature, heat of reaction and recovery strain increases with the increase of hafnium and tantalum content. A stable high temperature shape memory effect was observed (Ms = 385–390 °C) during the two thermal cycles between 20 °C and 725 °C. Transformation temperatures and heats of reaction were determined by DSC measurements. Recovery strain was determined by three-point bend testing. Also an alloy, 70Ti-26Ta-4Hf, with higher tantalum content was produced to observe the effect of Ta on the shape memory properties. Permeability increases gradually from 1.671 to 1.919 with increasing content of hafnium modification and remains stable in the frequency range of 450 MHz to 1 GHz.

Viscoelastic behavior of epoxy resin reinforced with shape-memory-alloy wires

2020 ◽  
pp. 1045389X2097549
Author(s):  
Niloufar Bagheri ◽  
Mahmood M Shokrieh ◽  
Ali Saeedi
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Epoxy Resin ◽  
Volume Fraction ◽  
Niti Alloy ◽  
Micromechanical Model ◽  
Viscoelastic Behavior ◽  
Mechanical Analysis ◽  
Reinforced Polymer ◽  
Small Volume Fraction

The effect of NiTi alloy long wires on the viscoelastic behavior of epoxy resin was investigated by utilizing the dynamic mechanical analysis (DMA) and a novel micromechanical model. The present model is capable of predicting the viscoelastic properties of the shape-memory-alloy (SMA) reinforced polymer as a function of the SMA volume fraction, initial martensite volume fraction, pre-strain level in wires, and the temperature variations. The model was verified by conducting experiments. Good agreement between the theoretical and experimental results was achieved. A parametric study was also performed to investigate the effect of SMA parameters. According to the results, by the addition of a small volume fraction of SMA, the storage modulus of the composite increases significantly, especially at higher temperatures. Moreover, applying a 4% pre-strain caused a 10% increase in the maximum value of the loss factor of the SMA reinforced epoxy in comparison with the 0% pre-strained SMA reinforced epoxy.

Studies on Thermomechanical Cycling Characteristics of an Ni-Ti-Cu Shape Memory Alloy

2021 ◽  
Vol 1016 ◽  
pp. 1538-1543
Author(s):  
Ganesan Swaminathan ◽  
Vedamanickam Sampath
Keyword(s):  
Shape Memory ◽  
Strain Recovery ◽  
Functional Characteristics ◽  
Functional Fatigue ◽  
Transformation Temperatures ◽  
Thermomechanical Cycling ◽  
Long Period ◽  
Recovery Strain ◽  
Number Of Cycles ◽  
Time In Service

Shape memory alloys (SMAs) find use in myriad medical and engineering applications. In these applications, the functional characteristics of the materials are capitalized on. SMAs are used repeatedly over a long period of time in service. With continued usage degradation occurs in their functional properties, leading to a change in recovery strain, recovery stress, phase transformation temperatures and hysteresis. The change in the functional characteristics of the alloys is known as functional fatigue. Functional fatigue affects the performance of the alloys with the alloys losing their intended functionality. This problem is to be addressed if the alloys are to be used effectively and efficiently throughout their lifespan. It is especially important when using the alloys within the human body, where such degradation can affect the performance of the biomedical devices and, in turn, human health and life. Till date not too many researchers have explored this area in greater detail. In order thereforeto better understand this behavior, in the present study, an Ni50Ti44.7Cu5.3 alloy wire with a d=1.43 mm and a l=100 mm was cycled (10,000) under constant stress (55 MPa) between its transformation temperatures, which were determined by DSC (without load). The effect of cycling on the shape memory properties (strain recovery, hysteresis, and transformation temperatures) after a specified number of cycles at regular intervals are considered. The results show that there is considerable difference in the properties obtained and are interpreted and discussed in detail in the paper.

Microstructure, Phase Stability, Mechanical Properties, and Shape Memory Characteristics of Ni-Fe-AI-B Alloys

1991 ◽  
Vol 246 ◽  
Author(s):  
E. P. George ◽  
C. T. Liu ◽  
C. J. Sparks ◽  
Ming-Yuan Kao ◽  
J. A. Horton ◽  
...  
Keyword(s):  
Shape Memory ◽  
Room Temperature ◽  
Cold Work ◽  
Second Phase ◽  
Scanning Calorimetry ◽  
Two Phase ◽  
Transformation Temperatures ◽  
Plate Morphology ◽  
Hot Rolled ◽  
Memory Characteristics

AbstractConventionally cast and hot-rolled Ni-Fe-AI-B alloys containing 4-20 at.% Fe, 23.9- 31.5 at.% Al, and 300 wppm B were investigated in this study. After oil quenching from 1300°C, all the alloys—except SMA-15 (27A1-14Fe)—have at least a two-phase microstructure, one phase of which is martensite with the characteristic plate morphology, and the other a globular second phase distributed throughout the microstructure. The amount of second phase generally increases with increasing Fe content. Alloys containing less than 14% Fe were found to be quite brittle at room temperature, indicating that a ductile second phase is at least partly responsible for the improved room-temperature ductility in the high-Fe alloys. The best tensile ductility (12%) was obtained in SMA-17 (23.9AI-20Fe) which was shown by X-ray diffraction to consist of 40% (mostly disordered) fcc [(Ni,Fe)3 (AI,Fe)] + 30% (partly ordered) bct martensite + 30% B2. Differential scanning calorimetry showed that the transformation temperatures for this alloy were MP = 65°C and AP = 95°C. Room-temperature tensile strains of 2-3% could be almost completely recovered in SMA-17 by heating for 3 min. at 600°C with the load removed. Upon subsequent cycling (i.e., strain-anneal cycling), the amount of strain recovery increased dramatically from 70% in the first cycle to nearly 100% after 4-5 cycles, indicating that cold work may help in improving the shape memory characteristics of this alloy. SMA-15 was found to have significantly higher transformation temperatures (Mp = 143°C and Ap = 170°C) than SMA-17; however, it is relatively brittle compared to SMA-17.

The Effect of Hafnium and Thermal Cycling on the Transformation Temperatures of NiTi-Based Shape Memory Alloys

1999 ◽  
Vol 604 ◽  
Author(s):  
Paul E. Thoma ◽  
John J. Boehm
Keyword(s):  
Shape Memory Alloys ◽  
Thermal Cycling ◽  
Shape Memory ◽  
Phase Transformations ◽  
Niti Alloy ◽  
Thermal Cycles ◽  
Transformation Temperatures

AbstractThe effect of thermal cycling on the austenite to martensite (A→M) and martensite to austenite (M→A) transformation temperatures (TTs) of Ni49.8Ti50.2 and Ni49.8Ti40.2Hf10 shape memory alloys is investigated. Test specimens are from arc melted buttons homogenized at 900°C for 100 hours. Results show that the A→M and M→A TTs for the alloys decrease with increasing number of thermal cycles through the phase transformations. The A→M TT of the NiTiHf alloy stabilizes more quickly than the A→M TT of the NiTi alloy when cycled. However, the M→A TT of the binary NiTi alloy stabilizes more quickly than the M→A TT of the NiTiHf alloy when cycled.

Effect of Aging Treatment on Phase Transformation of a Pseudoelastic NiTi Alloy

2014 ◽  
Vol 936 ◽  
pp. 1216-1223 ◽  
Author(s):  
Palloma Viera Muterlle ◽  
Eduard Benavides Villamarin ◽  
Paulo Herrera ◽  
Edson Paulo da Silva
Keyword(s):  
Phase Transformation ◽  
Shape Memory ◽  
Room Temperature ◽  
Niti Alloy ◽  
Aging Treatment ◽  
Single Step ◽  
Treatment Temperature ◽  
Scanning Calorimetry ◽  
Transformation Temperatures ◽  
X Ray

The pseudoelasticity (PE) and shape memory effect (SME) are the two main behaviors presented by the shape memory alloys (SMA's) and are associated respectively to mechanical and thermally induced martensitic transformations. The aim of this work is to investigate the effects of heat treatment temperature on the microstructure properties and phase transformation temperatures of a NiTi alloy with 57 w.t. % Ni. The X-ray diffraction (XRD) was carried out to obtain the phases present. The phase transformation temperatures were measured by differential scanning calorimetry (DSC). The alloy chemical composition and hardness were obtained by X-ray fluorescence (XRF), hardness (HRC) and microhardness (HV) tests, respectively. The analysis were performed in the state as received and after aging treatment at different temperatures between 350 °C and 600°C. The samples as received contained a fully austenitic microstructure at room temperature and the DSC analysis showed the presence of a phase transformation in multiple steps (B19'-R-B2). After aging at 350 °C the R phase was observed at room temperature with the austenite. With the aging treatment at 600 °C the R phase was solubilized and the alloy phase transformation occurred in a single step, ie, direct transformation from austenite to martensite and vice versa. The transformation temperatures Af, As, Ms and Mf changed with the aging treatment temperatures.

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