Inclusion control and fatigue properties of NiTi wires for medical applications

Superelastic wires of shape memory alloys are used for medical devices, but there has not been a systematic study about the correlations between fatigue properties and inclusion content. In this study we present a thorough investigation about the fatigue properties of 0.3 mm nitinol wires subjected to rotating bending fatigue. A comprehensive experimental campaign was conducted involving tests at different strain amplitudes for obtaining fatigue curves. The fracture surfaces of failed wires were analyzed through scanning electron microscopy, and data regarding the presence of particles and their morphology were recorded. We show qualitatively how inclusion dimensions affect fatigue. Finally, by means of extreme value statistics, we rate the particle dimensions of the four processes and correlate them to fatigue performance