TY - JOUR

T1 - Degradation of two-way shape memory effect due to the relaxation of internal oriented stress in NiTi alloy on holding at 640÷700 K

AU - Ponikarova, Irina

AU - Belyaev, Sergey

AU - Resnina, Natalia

PY - 2019/11/1

Y1 - 2019/11/1

N2 - This work aims to study the two-way shape memory effect degradation due to stress relaxation during holding pre-deformed Ni-50.0 at.% Ti alloy at temperatures from a range of 640–700 K. To initiate the two-way shape memory effect, samples were subjected to 12% preliminary isothermal deformation by torsion in the martensitic state (at room temperature). The influence of holding at 640 or 700 K for 0–60 min on the recoverable strain variation on cooling and heating of the pre-deformed samples was studied. The main degradation of the two-way shape memory effect was found after holding the sample up to 60 min; however, full degradation was not observed, even after holding at 700 K for 6 h. A decrease in the two-way shape memory effect value was believed to be caused by relaxation in the oriented internal stress and it was assumed that this process might be described by a first-order differential equation. This equation was used to simulate the influence of holding duration on the recoverable strain variation and a good correlation between the simulated and experimental data was obtained. The activation energy of the internal stress relaxation during holding at 640 or 700 K was calculated and found to be 0.84 ± 0.01 eV, which was close to the energy of vacancy migration.

AB - This work aims to study the two-way shape memory effect degradation due to stress relaxation during holding pre-deformed Ni-50.0 at.% Ti alloy at temperatures from a range of 640–700 K. To initiate the two-way shape memory effect, samples were subjected to 12% preliminary isothermal deformation by torsion in the martensitic state (at room temperature). The influence of holding at 640 or 700 K for 0–60 min on the recoverable strain variation on cooling and heating of the pre-deformed samples was studied. The main degradation of the two-way shape memory effect was found after holding the sample up to 60 min; however, full degradation was not observed, even after holding at 700 K for 6 h. A decrease in the two-way shape memory effect value was believed to be caused by relaxation in the oriented internal stress and it was assumed that this process might be described by a first-order differential equation. This equation was used to simulate the influence of holding duration on the recoverable strain variation and a good correlation between the simulated and experimental data was obtained. The activation energy of the internal stress relaxation during holding at 640 or 700 K was calculated and found to be 0.84 ± 0.01 eV, which was close to the energy of vacancy migration.

KW - эффект обратимой памяти формы, релаксация внутренних напряжений, NiTi

KW - Degradation

KW - NiTi

KW - Stress relaxation

KW - Two-way shape memory effect

KW - TWSME

KW - MARTENSITE DEFORMATION

KW - TRANSFORMATION TEMPERATURES

KW - STABILITY

KW - TINI

KW - HEAT-TREATMENT

KW - SMA ACTUATORS

UR - https://www.sciencedirect.com/science/article/pii/S0167663619302480

U2 - https://doi.org/10.1016/j.mechmat.2019.103174

DO - https://doi.org/10.1016/j.mechmat.2019.103174

M3 - Article

VL - 138

JO - Mechanics of Materials

JF - Mechanics of Materials

SN - 0167-6636

M1 - 103174

ER -