Mechanical properties of Ti–Ni Shape Memory Alloys in Micro-nano Scale

Pseudoelasticity 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 pseudoelastic behavior at the micro-nano scale is sparse. Recent demands for micro- and nano-electro-mechanical systems (MEMS and NEMS) have prompted the studies of pseudoelasticity of SMA at the micro-nano scale. In the present study, we developed TiNi-based SMAs for applications at the micro-nano scale, such as the actuators. To achieve this, we processed three TiNi-based SMAs, Ti49.05Ni50.95, Ti49.49Ni49.71Fe0.8 and Ti49.93Ni50.07, which had different austenite finish temperatures of –29.2 ºC, 10.0 ºC and 95.1 ºC, respectively. Nanoindentations performed on Ti49.05Ni50.95 and Ti49.49Ni49.71Fe0.8 at room temperature and different peak loads revealed the pseudoelastic behavior. For Ti49.93Ni50.07, nanoindentations performed at various temperatures showed different degrees of pseudoelasticity because of the different amounts of stress-induced martensitic transformation taking place during the indentation process. In addition to performing nanoindentation to study the localized pseudoelastic behavior of TiNi-based SMAs at the nano scale, micropillar compression tests were also performed to study the global pseudoelastic behavior. The findings of this work demonstrate the potential of integrating TiNi-based SMAs into MEMS and NEMS components that exhibit pseudoelasticity which, in turn, would result in a new generation of functional micro- and nanodevices.