Long Cycling Superelastic Behavior of Shape Memory Alloys for Potential MEMS Applications

Shape memory alloys offer the highest workout per unit of volume, in comparison with other functional materials. As a consequence they become more competitive when decreasing the size of the device, and then they are targeted for potential applications as sensors and actuators in Micro Electro-Mechanical Systems (MEMS). Recently it has been shown that Cu-Al-Ni exhibit good shape memory and superelastic behavior at micro and nano scale (J. San Juan et al., Adv. Mat. 20 (2008) 272, and Nature Nanotech. 4 (2009) 415), exhibiting advantageous Behavior over the Ti-Ni at small scale. However, for practical applications the superelastic behavior must be reproducible over hundred or thousand of cycles, in order to be functionally reliable.

A complete study of the superelastic cycling at micro and nano scale on Cu-Al-Ni SMA will be presented in the present work. Different pillars and arrays of pillars have been milled, by using the focused ion beam technique, being further tested during cycling by nano-compresion tests in an instrumented nanoindenter.

Fully recoverable and reproducible superelastic behavior has been obtained during long term cycling tests above thousand cycles. These promising results open the door for designing potential applications doing use of 3D devices of SMA, which could be integrated in MEMS technology.