Exceptional resilience of small-scale Au_(30)Cu_(25)Zn_(45) under cyclic stress-induced phase transformation

Abstract

Shape memory alloys that produce and recover from large deformation driven by martensitic transformation are widely exploited in biomedical devices and micro-actuators. Generally their actuation work degrades significantly within first a few cycles, and is reduced at smaller dimensions. Further, alloys exhibiting unprecedented reversibility have relatively small superelastic strain, 0.7%. These raise the questions of whether high reversibility is necessarily accompanied by small work and strain, and whether high work and strain is necessarily diminished at small scale. Here we conclusively demonstrate that these are not true by showing that Au_(30)Cu_(25)Zn_(45) pillars exhibit 12 MJ m^(−3) work and 3.5% superelastic strain even after 100,000 phase transformation cycles. Our findings confirm that the lattice compatibility dominates themechanical behavior of phase-changing materials at nano to micron scales, and points a way for smart micro-actuators design having the mutual benefits of high actuation work and long lifetime.

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