Shape memory behavior of nanostructured Ti-Ni alloy

Abstract
The paper focuses on the study of the shape memory effect (SME) and two-way SME (TWSME) in nanostructured Ti-50.7 at.%Ni alloy. Two different types of structure were studied: nano-subgrain structure (after the moderate deformation with true strain e = 0.3) and nanocrystalline structure (after the severe plastic deformation with true strain e = 1.55). The homogenizing annealing at 700 deg, 20 min as well served as a reference heat treatment (RHT). In all cases isothermal annealing at 430-450 deg. was performed. The aging time, the initial phase state and external action parameters were varied. The SME training procedure was carried out under a bending mode; the constrained strain ε_t was varied from 3.9 to 25% and the loading time from 30 s to 3 min. Aging time, constrained strain and loading time strongly affect all studied SME and TWSME parameters. The combined effect of 10 h –aging, loading through B2→R→B19’ transformation and 15,0 − 17,5% loading strain bring the highest combination of the recovery strain ε_r and the two-way shape memory effect ε_TW in the first training sycle. Multicycle training procedure does not bring significant changes. Variation of training parameters enables additional precise regulation of final functional properties. The obtained results can be used for development elements functioning in conditions of the SME and TWSME manifestation.