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.

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.

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.

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.

Effect of heat treatment on microstructure, corrosion, and shape memory characteristics of laser deposited NiTi alloy

2018 ◽  
Vol 744 ◽  
pp. 337-346 ◽  
Author(s):  
Jithin J. Marattukalam ◽  
Vamsi K. Balla ◽  
Mitun Das ◽  
Srikanth Bontha ◽  
Sreeram K. Kalpathy
Keyword(s):  
Heat Treatment ◽  
Shape Memory ◽  
Niti Alloy ◽  
Memory Characteristics

A Measurement of Volume Resistivity in Fe-Based Shape Memory Alloy under Tensile Deformation and its Evaluation of Strain Rate Sensitivity

2016 ◽  
Vol 725 ◽  
pp. 72-76 ◽  
Author(s):  
Bo Cao ◽  
Yutaro Moriyama ◽  
Kazuki Fujita ◽  
Takeshi Iwamoto
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
High Speed ◽  
Volume Fraction ◽  
Tensile Deformation ◽  
Niti Alloy ◽  
Rate Sensitivity ◽  
Volume Resistivity ◽  
Strain Rates ◽  
Vibration Absorbers

Fe-based shape memory alloy (Fe-SMA) shows the smaller shape memory effect (SME) compared with the widely-used NiTi alloy. However, because its production cost is much lower than the NiTi alloy, Fe-SMA is challenged to be applied in civil engineering fields such as vibration absorbers and joints. A key of the SME is stress-induced martensitic transformation. Thus, it is important to evaluate an amount of martensite, which can control such excellent performance of Fe-SMA, for increasing a reliability of the Fe-SMA. However, until now, it is quite hard to find studies to evaluate the amount of martensite in Fe-SMA experimentally during deformation at various strain rates, especially during high speed deformation. Instead of the evaluation, it is convenient to capture change in volume resistivity, which has a correlation with the amount of martensite, at various strain rates. In the past, the volume fraction of α’ martensite is evaluated by using a resistance measurement based on the four point-probes method. The advantages of the method are quite simple and relatively high precision, however, its disadvantages are a requirement of strictly-precise reference resistor and power supply, and it is easily affected from noise. In this study, at first, a circuit of Kelvin double bridge with a higher precision is assembled. Then, the rate sensitivity of volume resistivity in Fe-28Mn-6Si-5Cr alloy, which is a kind of Fe-SMA, is experimentally estimated by using the assembled circuit of Kelvin double bridge during tensile testing at various strain rates.

Study on the Two-Way Shape Memory Characteristics Induced by Compressive Loading Cycles

2010 ◽  
Vol 123-125 ◽  
pp. 1023-1026
Author(s):  
Young Ik Yoo ◽  
Jung Ju Lee
Keyword(s):  
Shape Memory ◽  
Niti Alloy ◽  
Compressive Loading ◽  
Memory Process ◽  
Recovery Stress ◽  
Maximum Deformation ◽  
Repetitive Loading ◽  
The One ◽  
Tubular Specimens ◽  
Memory Characteristics

The NiTi alloy can be trained by repetitive loading or heating cycles. As a result of the training, a two-way shape memory effect (TWSME) can be induced. Considerable research has been reported regarding the TWSME trained by tensile loading, however the TWSME trained by compressive loading has not been investigated nearly as much. In this research, six types of specimens (one solid cylindrical and five tubular) were used to obtain the two-way shape memory strain and two-way recovery stress and to evaluate the actuating capacity. The two-way actuating strain showed a saturated tendency after several training cycles for the same maximum deformation. A maximum value of the two-way strain was obtained for 7% of maximum deformation, independently of the geometry of the tubular specimens. The two-way strains obtained by the shape memory cycles and two-way recovery stress linearly increase as a function of the maximum deformation and the two-way strain, respectively, and the geometry of specimen affects the two-way recovery stress. Although the results show that sufficient recovery stress can be generated by either the two-way shape memory process or by the one-way shape memory process, the two-way shape memory process can be applied more conveniently to actuating applications.

scholarly journals Net-Shape NiTi Shape Memory Alloy by Spark Plasma Sintering Method

2021 ◽  
Vol 11 (4) ◽  
pp. 1802
Author(s):  
Sneha Samal ◽  
Orsolya Molnárová ◽  
Filip Průša ◽  
Jaromír Kopeček ◽  
Luděk Heller ◽  
...  
Keyword(s):  
Shape Memory ◽  
Shape Memory Effect ◽  
Spark Plasma Sintering ◽  
Memory Effect ◽  
Niti Alloy ◽  
Niti Shape Memory Alloy ◽  
Good Shape ◽  
Plasma Sintering ◽  
Shape Memory Effects ◽  
Spark Plasma

An analysis of the shape memory effect of a NiTi alloy by using the spark plasma sintering approach has been carried out. Spark plasma sintering of Ti50Ni50 powder (20–63 µm) at a temperature of 900 °C produced specimens showing good shape memory effects. However, the sample showed 2.5% porosity due to a load of 48 MPa. Furthermore, an apparent shape memory effect was recorded and the specimens were characterized by uniformity in chemical composition and shape memory alloys of NiTi showed significant austenite phases with a bending strain recovery of >2.5%.

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