A Comparative Study of Structure Formation in Thermomechanically Treated Ti-Ni and Ti-Nb-(Zr, Ta) SMA

The processes of structure formation in Ti-Ni and in Ti-Nb-Zr, Ti-Nb-Ta shape memory alloys (SMA) under thermomechanical treatment (TMT) were studied. The TMT comprised cold rolling with true strains from e=0.25 to 2 and post-deformation annealing. Differences in these processes between two groups of alloys are considered. The main conclusions are as follows: nanostructures created by TMT are useful for radical improvement of the SMA functional properties, and an optimum nanostructure (nanocrystalline structure, nanosubgrained structure or theirmixture) should be selected by taking into account other structural and technological factors.

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Comparative study of structure formation and mechanical behavior of age-hardened Ti–Nb–Zr and Ti–Nb–Ta shape memory alloys

Materials Characterization ◽

10.1016/j.matchar.2015.03.016 ◽

2015 ◽

Vol 103 ◽

pp. 65-74 ◽

Cited By ~ 25

Author(s):

K. Inaekyan ◽

V. Brailovski ◽

S. Prokoshkin ◽

V. Pushin ◽

S. Dubinskiy ◽

...

Keyword(s):

Comparative Study ◽

Shape Memory Alloys ◽

Mechanical Behavior ◽

Shape Memory ◽

Structure Formation

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Functional Properties of Ti-Ni-Based Shape Memory Alloys

Advances in Science and Technology ◽

10.4028/www.scientific.net/ast.59.156 ◽

2008 ◽

Vol 59 ◽

pp. 156-161 ◽

Cited By ~ 3

Author(s):

I. Khmelevskaya ◽

Sergey Prokoshkin ◽

Vladimir Brailovski ◽

K.E. Inaekyan ◽

Vincent Demers ◽

...

Keyword(s):

Grain Size ◽

Cold Rolling ◽

Shape Memory Alloys ◽

Shape Memory ◽

Functional Properties ◽

High Pressure Torsion ◽

Martensitic Transformations ◽

Critical Temperatures ◽

Recoverable Strain ◽

Ultrafine Grained

The main functional properties (FP) of Ti-Ni Shape Memory Alloys (SMA) are their critical temperatures of martensitic transformations, their maximum completely recoverable strain (er,1 max) and maximum recovery stress (sr max). Control of the Ti-Ni-based SMA FP develops by forming well-developed dislocation substructures or ultrafine-grained structures using various modes of thermomechanical treatment (TMT), including severe plastic deformation (SPD). The present work shows that TMT, including SPD, under conditions of high pressure torsion (HPT), equal-channel angular pressing (ECAP) or severe cold rolling followed by post-deformation annealing (PDA), which creates nanocrystalline or submicrocrystalline structures, is more beneficial from SMA FP point of view than does traditional TMT creating well-developed dislocation substructure. ECAP and low-temperature TMT by cold rolling followed by PDA allows formation of submicrocrystalline or nanocrystalline structures with grain size from 20 to 300 nm in bulk, and long-size samples of Ti-50.0; 50.6; 50.7%Ni and Ti-47%Ni-3%Fe alloys. The best combination of FP: sr max =1400 MPa and er,1 max=8%, is reached in Ti-Ni SMA after LTMT with e=1.9 followed by annealing at 400°C which results in nanocrystalline (grain size of 50 to 80 nm) structure formation. Application of ultrafine-grained SMA results in decrease in metal consumption for various medical implants and devices based on shape memory and superelastiсity effects.

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