Characterization of NiTi Inclusions

Inclusions content is important for the mechanical behavior and performances of Nitinol wires particularly in fatigue rated devices. Higher inclusions content has been correlated to reductions in transformation temperatures and strain recovery under mechanical or thermo-mechanical cycling. Moreover, most fatigue fractures show inclusions at the initiation site. However, there is a general lack of information on the nature and characteristics of such inclusions, especially those typically recognized as intermetallics oxides. In this work, the common microscopy techniques and nanoindentation have been used to investigate the microstructural and mechanical properties of inclusions in commercial standard binary NiTi wires. Preliminary results and their significance will be presented and discussed.