Superelasticity of TiNi-based shape memory alloys at micro/nanoscale

Superelasticity of shape memory alloy (SMA) results from the reversible thermoelastic martensitic transformation. Although this property has been studied extensively at the macroscale, the study of this superelastic behavior at the micro/nanoscale is relatively new. In this work, we processed TiNi-based SMAs with different compositions and different phase transformation temperatures. Nanoindentations were performed with different peak loads and at various temperatures to systematically characterize the degree of localized stress-induced martensitic transformation at the nanoscale for each SMA. Micropillar compression tests were also performed to study the global superelastic behavior at the microscale. The physics of stress-induced martensitic transformation versus the phase transformation temperature, the testing temperature, and the peak load relations was explored and the difference between the localized and the global superelastic behaviors was discussed. Our results demonstrate the potential of integrating TiNi-based SMAs into functional micro- and nanodevices.