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.
Structural Change in Ni-Fe-Ga Magnetic Shape Memory Alloys after Severe Plastic Deformation
