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

Abstract

The influence of increased dislocation density; dispersity of Ni-rich (Ti3Ni4and Ti2Ni3) particles and volume fraction of Ti-rich (Ti2Ni) 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 may be improved by increasing the part of deformation which is realized by martensitic mechanism. This part may be estimated by measuring εcr, which can reflect the influence of the structure parameter both on σMand σslip. It was found that in high-cycle fatigue conditions 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).