Nanocomposite NiTi shape memory alloy with high strength and fatigue resistance

The source data is uploaded to support our publication in Nature Nanotechnology (DOI: https://doi.org/10.1038/s41565-020-00837-5). Citation is required for using the data.<br>AbstractFatigue life enhancement of NiTi-based shape memory alloys (SMA) has been an active topic over the past decades, because many established and potential applications of NiTi SMA in biomedical devices and recent solid-state refrigeration require very long fatigue life (10⁷-10⁹). However, improving the fatigue resistance of NiTi often compromises other mechanical and functional properties. Here we provide a new strategy to overcome this dilemma through hybrid heterogenous nanostructure. We produced superelastic NiTi nanocomposite with crystalline and amorphous phases via severe plastic deformation and low temperature annealing. We show that the NiTi nanocomposite has a recoverable strain of 4.3%, yield strength of 2.3 GPa, and can endure over 10⁸ reversible-phase-transition cycles under the stress of 1.8 GPa via compression experiments of micropillars. We attribute the enhanced properties to the mutual strengthening of nano-sized amorphous and crystalline phases where both dislocation slip in the crystals and shear band propagation in the amorphous phase are suppressed. The synergy of the properties of crystalline and amorphous phases at the nanoscale could be an effective method to improve fatigue resistance and strength of SMA.