Bimodal scaling law and size effect in superelastic nanopillars

Shape memory alloys that can deform and then spring back to their original shape, have found a wide range of applications in the medical field, from heart valves to stents. As we push the boundaries of technology creating smaller, more precise tools for delicate surgery treatments, the behavior of these alloys at tiny scales becomes increasingly crucial. In this study, we discover that the size effect of critical stress required for stress-induced phase transformation is not universal. We propose an orientation-dependent power decay law, indicating a specific increase in critical stress for pillars smaller than 1 micrometer for the nominally soft [001] and hard [111] orientations. Additionally, we observe high transformability with 11% recoverable strain under high stress (2 GPa) through lattice frustration at 200 nm scale. This research opens new avenues for exploring the superior elastic behavior of shape memory alloys for nanodevices.