Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
International Journal of Materials Research, Jun 1, 2004
The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory... more The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory alloys affect their mechanical and functional properties. In the present work precipitate sizes and volume fractions were measured after various thermo-mechanical treatments using transmission electron microscopy (TEM) in combination with quantitative metallography. TEM tilting experiments revealed that the Ni4Ti3 particles have a disk-like shape with a disk diameter D and a disk thickness t. These two parameters together with the number density of particles per unit volume were determined after stress-free and stress-assisted aging at 400, 500 and 530 °C. Volume fraction results are presented after different thermo-mechanical treatments and our quantitative metallographic procedure is documented.
In this study, the influences of the stress aging process on the electrochemical behaviors toward... more In this study, the influences of the stress aging process on the electrochemical behaviors toward evaluating corrosion resistance of NiTi shape memory alloys in the in-vitro condition have been investigated. For this approach, the samples have been manufactured by introducing multiple precipitation morphology in the alloy structure via applying different levels of stresses during the aging process. The samples were characterized using multiply electron microscopy, electrochemical methods, X-ray diffraction, and differential scanning calorimetry. Results show that by prolonging aging time from 1 to 5 h and increasing the stress aging level (15–60-150 MPa) the corrosion resistance improves, which is implied a better formation of a protective layer. It seems that homogeneous precipitation of Ni-rich phases under the stress aging process improves the corrosion resistance of the alloy.
NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of ... more NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of the thermo-elastic and the reversible martensitic transformation [13]. The high-temperature phase austenite with the B2 struc-ture, on cooling, transforms to low-temperature phase ...
Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
International Journal of Materials Research, Jun 1, 2004
The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory... more The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory alloys affect their mechanical and functional properties. In the present work precipitate sizes and volume fractions were measured after various thermo-mechanical treatments using transmission electron microscopy (TEM) in combination with quantitative metallography. TEM tilting experiments revealed that the Ni4Ti3 particles have a disk-like shape with a disk diameter D and a disk thickness t. These two parameters together with the number density of particles per unit volume were determined after stress-free and stress-assisted aging at 400, 500 and 530 °C. Volume fraction results are presented after different thermo-mechanical treatments and our quantitative metallographic procedure is documented.
In this study, the influences of the stress aging process on the electrochemical behaviors toward... more In this study, the influences of the stress aging process on the electrochemical behaviors toward evaluating corrosion resistance of NiTi shape memory alloys in the in-vitro condition have been investigated. For this approach, the samples have been manufactured by introducing multiple precipitation morphology in the alloy structure via applying different levels of stresses during the aging process. The samples were characterized using multiply electron microscopy, electrochemical methods, X-ray diffraction, and differential scanning calorimetry. Results show that by prolonging aging time from 1 to 5 h and increasing the stress aging level (15–60-150 MPa) the corrosion resistance improves, which is implied a better formation of a protective layer. It seems that homogeneous precipitation of Ni-rich phases under the stress aging process improves the corrosion resistance of the alloy.
NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of ... more NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of the thermo-elastic and the reversible martensitic transformation [13]. The high-temperature phase austenite with the B2 struc-ture, on cooling, transforms to low-temperature phase ...
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