scholarly journals Influence of alloying elements on the thermal behavior of NiTi shape memory alloys

2021 ◽  
Vol 342 ◽  
pp. 06007
Author(s):  
Nicoleta-Monica Lohan ◽  
Çtefan-Lucian Toma ◽  
Mihai Popa ◽  
Alin Marian Cazac ◽  
Bogdan Pricop
Keyword(s):  
Shape Memory Alloys ◽  
Thermal Behavior ◽  
Shape Memory ◽  
Alloying Elements ◽  
Alloying Element ◽  
Scanning Calorimetry ◽  
Automotive Manufacturing ◽  
Niti Alloys ◽  
The Third ◽  
Niti Shape Memory Alloys

NiTi based shape memory alloys are one of the most intensely studied alloys from its class. Therefore, diverse commercial applications have been developed due to certain properties such as: shape memory effect, superelasticity and corrosion resistance. Currently, the main applications of NiTi alloys are automotive manufacturing and aerospace actuators, biomedical devices or pipe couplings. In recent years, NiTi shape memory alloys have been alloyed with a third element in order to improve the above-mentioned properties. In order to investigate the influence of the alloying elements on the thermal behavior of NiTi alloys, the addition of the third alloying element (Ta and Nb) is under investigation in the present study. The thermal behavior of the three alloys (NiTi, NiTiNb and NiTiTa) was studied by differential scanning calorimetry. Following the experiments, it was observed that the addition of the third alloying element influences the critical transformation temperatures.

Cast NiTi Shape-Memory Alloys

2004 ◽  
Vol 855 ◽  
Author(s):  
Alicia M. Ortega ◽  
Carl P. Frick ◽  
Jeffrey Tyber ◽  
Ken Gall ◽  
Hans J. Maier
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Grain Orientation ◽  
Mechanical Response ◽  
Complex Geometry ◽  
Low Cost ◽  
Orientation Distribution ◽  
Scanning Calorimetry ◽  
Cast Material ◽  
Niti Shape Memory Alloys

ABSTRACTThe purpose of this study is to investigate the structure and properties of polycrystalline NiTi in its cast form. Although it is commonly stated in the literature that cast NiTi has poor shape-memory behavior, this study demonstrates that with appropriate nano/micro structural design, cast NiTi possesses excellent shape-memory properties. Cast NiTi shape-memory alloys may give rise to a new palette of low-cost, complex-geometry components. Results from two different nominal compositions of cast NiTi are presented: 50.1 at.%Ni and 50.9 at.%Ni. The cast NiTi showed a spatial variance in grain size and a random grain orientation distribution throughout the cast material. However, small variances in the thermo-mechanical response of the cast material resulted. Transformation temperatures were slightly influenced by the radial location from which the material was extracted from the casting, showing a change in Differential Scanning Calorimetry peak diffuseness as well as a change in transformation sequence for the 50.9 at.%Ni material. Mildly aged 50.9 at.%Ni material was capable of full shape-memory strain recovery after being strained to 5% under compression, while the 50.1 at.%Ni demonstrated residual plastic strains of around 1.5%. The isotropic and symmetric response under tensile and compressive loading is a result of the measured random grain orientation distribution. The favorable recovery properties in the cast material are primarily attributed to the presence of nanometer scale precipitates, which inhibit dislocation motion and favor the martensitic transformation.

Multi-stage martensitic transformation in Ni-rich NiTi shape memory alloys

2017 ◽  
Vol 10 (01) ◽  
pp. 1740004 ◽  
Author(s):  
Xiebin Wang ◽  
Bert Verlinden ◽  
Sergey Kustov
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Precipitation Hardening ◽  
Aging Treatment ◽  
Functional Stability ◽  
Transformation Behavior ◽  
Niti Alloys ◽  
Multi Stage ◽  
Niti Shape Memory Alloys

Precipitation hardening is an effective way to improve the functional stability of NiTi shape memory alloys. The precipitates, mainly Ni4Ti3, could be introduced by aging treatment in Ni-rich NiTi alloys. However, the presence of Ni4Ti3 precipitates could disturb the transformation behavior, resulting in the multi-stage martensitic transformation (MMT). With the presence of MMT, it is difficult to control the transformation behavior, and thus limits the applicability of NiTi alloys. In this work, previous efforts on explaining the observed MMT are summarized. The difficulties in developing a unified explanation are discussed, and a possible way to avoid the MMT is proposed.

scholarly journals Continuous Heating Dissolution and Continuous Cooling Precipitation Diagrams of a Nickel-Titanium Shape Memory Alloy

2021 ◽  
Author(s):  
Christian Rowolt ◽  
Benjamin Milkereit ◽  
Jette Broer ◽  
Armin Springer ◽  
Olaf Kessler
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensite Transformation ◽  
Continuous Heating ◽  
Solution Annealing ◽  
Scanning Calorimetry ◽  
Transformation Temperatures ◽  
Niti Alloys ◽  
Continuous Cooling ◽  
Precipitation Processes

AbstractBinary NiTi alloys are the most common shape memory alloys in medical applications, combining good mechanical properties and high biocompatibility. In NiTi alloys, the shape memory effect is caused by the transformation of an austenite phase to a martensite phase and the reverse process. Transformation temperatures are strongly influenced by the exact chemical composition of the NiTi phase and the presence of precipitates in the microstructure induced by thermo-mechanical treatment, especially solution annealing and ageing. Isothermal time–temperature precipitation diagrams can be found in the literature. Cooling is frequently not considered, as water quenching is typically assumed to be sufficient. To the best of our knowledge, continuous heating dissolution (CHD) and continuous cooling precipitation (CCP) diagrams do not exist. Differential scanning calorimetry (DSC) is a common method to analyse the austenite/martensite transformation in shape memory alloys, but it has not yet been used to analyse precipitation processes during continuous temperature changes. We have enabled DSC to analyse dissolution and precipitation processes in situ during heating as well as during cooling from the solution annealing temperature. Results are presented as CHD and CCP diagrams, including information from microstructure analysis and the associated changes in the austenite/martensite transformation temperatures.

scholarly journals Effect of ambient temperature on compressibility and recovery of NiTi shape memory alloys as static seals

2017 ◽  
Vol 9 (2) ◽  
pp. 168781401769228 ◽  
Author(s):  
Xiaofeng Lu ◽  
Gang Li ◽  
Luwei Liu ◽  
Xiaolei Zhu ◽  
Shan-Tung Tu
Keyword(s):  
Shape Memory Alloys ◽  
Ambient Temperature ◽  
Shape Memory ◽  
Residual Strain ◽  
Recovery Coefficient ◽  
Compression Loading ◽  
Finish Temperature ◽  
Niti Alloys ◽  
Niti Shape Memory Alloys ◽  
Martensite Reorientation

The objective of this study was to investigate the effect of ambient temperature on compressibility and recovery of NiTi shape memory alloys as static seals. Experimental results indicated that compressibility and recovery of NiTi alloys were dependent on ambient temperature. At T < Af (the austenite finish temperature), the compressibility and recovery coefficients were almost unchanged when the compression stress was higher than a certain level. The residual strain of NiTi alloys increased with a decrease in temperature at T < Af. The residual strain of NiTi alloys was remarkably high at the temperature below Mf (the martensite finish temperature). The recovery coefficient of NiTi alloys at T > Af gradually increased with increasing compression loading. The compressibility and recovery coefficients of NiTi alloys were insignificantly fluctuated at the temperatures between 60°C and 150°C upon the compression loading. The features of strong deformation and martensite reorientation in the compressed NiTi alloys confirmed the temperature effect.

THERMAL PARAMETERS AND STRUCTURAL INVESTIGATIONS OF Cu-BASED SHAPE MEMORY ALLOYS IRRADIATED WITH Co-60

2021 ◽  
Vol 8 (18) ◽  
pp. 151-164
Author(s):  
Şahide Nevin BALO ◽  
Abdulvahap ORHAN
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Thermodynamic Parameters ◽  
Structural Properties ◽  
Functional Materials ◽  
Optical Microscope ◽  
Alloying Elements ◽  
Nuclear Facilities ◽  
Scanning Calorimetry ◽  
Structural Investigations

Gamma radiation is a type of radiation that can change the structural properties of materials. Many physical and structural properties of metals and alloys change due to defects in their crystal structures in response to irradiation. Shape memory alloys (SMAs) are functional materials and are used in mechanical devices for monitoring nuclear facilities. In this study, copper-based SMAs were used. Copper-based SMAs are very sensitive to alloying elements and small changes in element percentages. Cu-11.6Al-0.42Be, Cu-11.8Al-0.47Be, Cu-13Al-4Ni, and Cu-13.5Al-4Ni (wt%) SMA samples were irradiated with a fixed radiation dose of 50 kGy. The effect of irradiation on the thermodynamic parameters and structural properties of copper-based SMAs was investigated. The effects of irradiation on thermodynamic parameters were determined by differential scanning calorimetry (DSC). Structural examinations were made by X-ray diffraction (XRD) and optical microscope observations. Microhardness measurements were taken. The results obtained for Cu-based SMAs were evaluated both as homogeneous and irradiated samples and according to alloying elements.

Effect of the linear velocity during the melt spinning process on shape memory transformation of Ni-Ti ribbons

2012 ◽  
Vol 1373 ◽  
Author(s):  
E. Nuñez-Mendoza ◽  
E. López Cuellar ◽  
Walman Benicio de Castro ◽  
B. López Walle
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Melt Spinning ◽  
Solidification Rate ◽  
Linear Velocity ◽  
Vacuum Induction Melting ◽  
Induction Melting ◽  
Scanning Calorimetry ◽  
Spinning Process ◽  
Niti Shape Memory Alloys

AbstractThe usual process to produce NiTi shape memory alloys is vacuum induction melting (VIM). Currently a new alternative process to produce NiTi shape memory alloys by rapid solidification structures called Melt Spinning has been studied. In this work, results of ribbons with a chemical composition Ti-55.2 Ni (wt %) alloy prepared by this method are presented. The ribbons are prepared at two different linear velocities: 30 m/s and 50 m/s. After that, samples are heat treated at 350 °C during 1 hour. The alloys are characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction. According to the cycled DSC test, transformation peaks are associated with the B2→R→B19´ transformation during cooling and B19´→R→B2 during heating, showing transformation in multi-peaks. The martensite B19´ start (Ms) is varying from 35 to 39°C and the martensite finish (Mf) from 15 to 21°C, 42-47°C for austenite B2 start (As) and 65-69°C for austenite finish (Af) approximately. All analyzed ribbons show very similar values of transformation hysteresis temperatures at 50% of transformation of around 28°C. In order to change solidification rate, linear velocity is varied during the melt spinning process. Results indicate that linear velocity affects directly the temperature of transformation. When the linear velocity is increasing, crystallographic Ti-rich precipitates are developed, but dendritic growth disappears, changing the microstructure and decreasing these transformation temperatures. Then changes in linear velocity can dramatically affect shape memory properties, and in this case a velocity of 50 m/s produces a more homogenous alloy.

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