Microstructure evolution during cyclic deformation of the nanocrystalline superelastic Ti-50.9 at .% Ni alloy with different parent phases

A comparative study of the effect of the initial state structure (B2-austenite or R-martensite) on the evolution of the deformation structure of the nanocrystalline superelastic alloy Ti-50.9 at. % Ni under cyclic tension in the loading-unloading mode up to 45 cycles was carried out in the laboratory of physical materials science of steels and alloys. It was established that dislocations accumulate in B2-austenite during cycling, followed by a change in the B2-austenite deformation mechanism. It has been shown that in the region of 10-20 cycles in B2-austenite there is a transition from the accumulation of dislocations to the mechanism of structure reorientation and the formation of deformation mesopoles. At the same time, it was found that the structure of the R-phase does not change qualitatively as the cycle progresses. It has been shown that the presence of the R-phase as the initial one is characterized by a low level of internal stresses (less than 100 MPa), prevents the formation of deformation bands and helps to increase the cyclic stability of the superelastic behavior of the alloy. It has been found that the R-martensite structure provides higher resistance to accumulation of defects during mechanical cycling compared to the B2-austenite structure, which helps to maintain relatively stable mechanical properties of the TiNi nanocrystalline alloy and maintain fatigue strength.
Published in Intermetallics 198 (2026) 109572 (IF 5.3, Q1)
https/doi.org/1016/j.intermet,2026.109572
The study was performed within the framework of the state assignment for the IFPM SB RAS (project No. FWRW-2026-0005).