Dr. Chun-Hway Hsueh
Department of Materials Science & Engineering,
National Taiwan University
11:00 a.m.–12:30 p.m. Wednesday,
August 6, 2014
"Studies of TiNi-based Shape Memory Alloys at Micro-nano Scale"
Superelasticity and shape memory effects of shape memory alloy (SMA) result from the reversible thermoelastic martensitic transformation. Although these properties have been studied extensively at the macro scale, the study at the micro-nano scale is relatively new.
Recent demands for micro- and nano-electro-mechanical systems (MEMS and NEMS) have prompted the studies 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 –28.5 ºC, 11.5 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 superelastic behavior. For Ti49.93Ni50.07, nanoindentations performed at various temperatures showed different degrees of superelasticity 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 superelastic behavior of Ti-Ni SMAs at the nano scale, micropillar compression tests were also performed to study the global superelastic behavior and shape memory effects.
The findings of this work demonstrate the potential of integrating Ti-Ni SMAs into MEMS and NEMS components that exhibit superelasticity which, in turn, would result in a new generation of functional micro- and nano-devices.