Influence of the Structure on the Strain-Controlled Fatigue of Nitinol

摘要

The influence of increased dislocation density; dispersity of Ni-rich (Ti_3Ni_4 and Ti_2Ni_3) particles and volume fraction of Ti-rich (Ti_2NiO_x) particles on the low-cycle (high amplitude) and high-cycle (low amplitude) fatigue resistance of nitinol has been considered in this paper. It was revealed that the fatigue resistance of nitinol in low-cycle conditions (N≤le3,ε_a≥2%) may be improved by increasing the part of deformation which is realized by martensitic mechanism. This part may be estimated by measuring ε_c~(0.2)r, which can reflect the influence of the structure parameter both on σ_M and σ_(slip). It was found that in high-cycle fatigue conditions (N≥le6, (ε_a≤0.5%) the substructure of nitinol predominantly determine its fatigue resistance, which is being the better in samples that had higher dislocation density or high dispersity of Ni-rich particles (up to 30 nm).