Stress-induced pseudoelasticity in freestanding Cu–Al–Ni thin film by AFM-assisted nanoindentation

Abstract

Freestanding thin films of Cu–Al–Ni shape memory alloys (SMAs) have attracted interests in recent years for the development of next generation micro-scaled sensors and actuators in MEMS. Thin films’ capacity to recover stress-induced strain is critical to assess their potential for applications in these technologies. In this work, we report for the first time a quantitative study of this capacity in a freestanding Cu–Al–Ni thin film by Atomic Force Microscopy (AFM)-assisted nanoindentation. Stress-induced pseudoelastic (or superelastic) effects were successfully observed by this technique for relatively high strains up to a relative indentation depth of 30% concerning the film thickness. This effect highlights a clear shape memory effect, suggesting a sample's high mechanical performance for potential applications in the design of micro actuators for MEMS technologies. Results enable to set new perspectives of the use of this technique as an efficient methodology for future study of pseudoelasticity in micro/nanostructured SMAs.