Fatigue Testing of a New Generation Commercial Scale Low Inclusion NiTi Alloy

The effects of inclusions within a Nitinol material on the fatigue performance has been largely accepted by the Nitinol community. With great improvements in material quality, the statistical probability of an inclusion being at the region of high stress and facilitating fatigue failure is much reduced. Scaling of low inclusion NiTi ingot production to suit commercial demands has been an ongoing challenge within the Nitinol industry. As presented in a separate talk, a new generation of commercial scale, low inclusion Nitinol material has been developed and proven through a comprehensive robustness protocol that assessed process variability and stability of physical and mechanical properties. The purpose of this study is to demonstrate the improved fatigue behavior that can be realized at the final device level when utilizing this new alloy.

In this study thermomechanical material characterization as well as rotating beam testing (RBT) and linear Z-specimen fatigue testing of a 0.021” wire drawn from this new generation low inclusion NiTi Alloy was performed. Through the use of both RBT, linear Z-speciman fatigue testing, both the zero mean strain and 3.5% mean strain conditions were challenged with strain amplitudes ranging from 2.5 to 0.5 %.

Through this work, the fatigue performance of Nitinol wireform devices created using this new generation low inclusion alloy has been benchmarked with respect to standard commercial NiTi alloys.