Abstract Scope |
Owing to its excellent strength, high corrosion resistance and biocompatibility combined with superelastic strain recovery, nitinol has found many applications in the aerospace and biomedical device industries. In most applications, nitinol components experience cyclic loads and a mixed state of austenite–martensite phases. Unfortunately, due to the complicated nature of the stress-induced martensitic transformations, the existing fatigue theories do not precisely address the fatigue crack nucleation, propagation, and eventual failure of superelastic components. It has been shown that other than surface defects, the internal microstructural inhomogeneities, such as non-metallic inclusions, also play a role in fatigue crack initiation. In this work, advanced non-destructive characterization techniques such as X-ray microtomography (μCT) and far-field high energy diffraction microscopy (ff-HEDM) are utilized to obtain the 3-D map of the inclusions, crystallographic orientation of the grains, and the lattice strain surrounding them before and during the fatigue test. |