Bimodal Scaling Law and Size Effect In Superelastic Nanopillars

TL;DR

This paper investigates the size-dependent behavior of superelastic shape memory alloy nanopillars, revealing a non-universal size effect and proposing an orientation-dependent scaling law that impacts their application in nanodevices.

Contribution

It introduces an orientation-dependent power decay law for critical stress and demonstrates high recoverable strain at nanoscale, advancing understanding of shape memory alloys at small sizes.

Findings

Critical stress increases for pillars smaller than 1 micron in specific orientations.

High recoverable strain of 11% at 200nm scale under 2 GPa stress.

Size effect is not universal but orientation-dependent.

Abstract

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 micron meter 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 200nm scale. This research opens new avenues for exploring the superior elastic behavior of shape memory alloys for nanodevices.