In situ neutron diffraction studies of the R-phase transformation in the NiTi shape memory alloy

2002 ◽  
Vol 74 (0) ◽  
pp. s1121-s1123 ◽  
Author(s):  
P. Luk�? ◽  
P. ?ittner ◽  
D. Lugovoy ◽  
D. Neov ◽  
M. Ceretti
Keyword(s):  
Phase Transformation ◽  
Neutron Diffraction ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Niti Shape Memory Alloy ◽  
In Situ Neutron Diffraction

scholarly journals In Situ Characterization of the Elasticity and Stress-Induced Phase Transformation of NiTi Shape-Memory Alloy

2018 ◽  
Vol 134 (3) ◽  
pp. 811-814
Author(s):  
T. Grabec ◽  
K. Zoubková ◽  
P. Stoklasová ◽  
M. Ševčík ◽  
P. Sedlák ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Niti Shape Memory Alloy

Heating and Loading Paths to Optimize the Performance of Trained Shape Memory Alloy Torsional Actuators

2016 ◽  
Author(s):  
Douglas E. Nicholson ◽  
Micheal A. Bass ◽  
James H. Mabe ◽  
Othmane Benafan ◽  
Santo A. Padula ◽  
...  
Keyword(s):  
Shape Memory Alloy ◽  
Thermal Cycling ◽  
Shape Memory ◽  
Niti Shape Memory Alloy ◽  
Martensite Variant ◽  
Load Paths ◽  
Martensitic State ◽  
The Stability ◽  
In Situ Neutron Diffraction

Near-equiatomic NiTi shape memory alloy (SMA) torsional tube actuators were trained for two-way shape memory effect (TWSME) by repeated thermal cycling under an isobaric load. Performance of the trained actuators was assessed by thermally cycling through a complete phase transformation under a range of isobaric loads that varied from negative to positive and included loads near zero. To assess the actuation performance of the trained SMA components, extended isobaric thermal cycling and cycling under varying loads to constant strain limits was performed. Additionally, isothermal loading was applied in the fully martensitic state prior to and following training. Results show stable TWSME when cycling under significant isobaric loading in the trained direction, however at low or negative loads (loads applied opposite to the training direction) a degradation of TWSME occurred during thermal cycling. Isothermal loading showed that martensite variant reorientation and detwinning was redistributed in the trained actuator when compared to an untrained actuator. Thermal cycling against constant strain limits was shown to have a negligible effect on the stability of the TWSME and overall performance of the trained actuator. Various combinations of isothermal and isobaric loading were shown to expand the operating range at low and negative loads. Additionally, load paths were identified which limit the degradation of TWSME over extended cycling. The aforementioned results are discussed in the context of the correlation between uniaxial isobaric and isothermal loading and texture measurements obtained by in-situ neutron diffraction at stress and temperature. These results show various thermomechanical combinations of heating and loading sequences that yield the same final martensite texture in SMA, which highlights the ability to take different paths yet still obtain the desired actuator response while minimizing irrecoverable deformation mechanisms. The implications of extending these uniaxial results to the design and fabrication and ultimately improving the performance of torsional SMA actuators are discussed.

Observation of Phase Transformation in Shape Memory Alloy NiTi Wire during In Vitro Simulation of Orthodontic Treatment

2015 ◽  
Vol 364 ◽  
pp. 61-70
Author(s):  
Rebeka Rudolf ◽  
Janko Ferčec
Keyword(s):  
Electron Microscopy ◽  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Electrical Resistance ◽  
Orthodontic Treatment ◽  
Niti Shape Memory Alloy ◽  
Niti Wire ◽  
Transmission Electron

The aim of this study was to simulate the different loadings on NiTi Shape Memory Alloy in the form of wire that occurs in orthodontic praxis. Our main goals were to detect and determine the beginning of the stress-induced transformation from the austenite to martensite phases and to indicate the transformation plateau at different deformations during orthodontic treatment usingin-vitrosimulation. For this reason, we developed two prototype devices forin-situsimulation of orthodontic treatment by which we measured the electrical resistance and hardness. Accompanying these two properties and the microstructure observations of loaded wires by Transmission Electron Microscopy enabled us to detect successfully the stabilized stress-induced martensite due phase transformation. We found out that transformation depends strongly on the type of loading.

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