Microstructure and structural fatigue of ultra-fine grained NiTi-stents

In the present study we characterize the microstructure of pseudoelastic, ultra-fine grained, Ni-rich NiTi-stents using transmission electron microscopy (TEM) and perform structural fatigue experiments. The TEM-samples were taken from small struts, the elementary building units of medical stents. They were prepared using a focused ion beam (FIB) system. Microstents were subjected to approximately 6000 cycles at room temperature in air at a frequency of 1 Hz. They were then integrated into an in situ test rig which allowed to perform cyclic tensile loading in a scanning electron microscope (SEM). The present paper reports the stress–strain response associated with cyclic loading and documents failure mechanisms.