Bistable Actuators Based on Shape Memory Alloy/ Polymer Composites

The thermal induced martensitic phase transition in TiNiHf was exploited for bi-directional actuation with TiNiHf/SiO2/Si composites. When compared to free-standing films of similar thickness, films on a substrate exhibit a reduced fatigue effect upon thermal cycling and a smaller hysteresis width. Differential scanning calorimetry (DSC) and cantilever deflection measurements (CDM) results showed that the transition temperatures of fabricated TiNiHf films and TiNiHf/SiO2/Si bimorph composites decrease with thermal cycling. The change in transition temperatures after 40 thermal cycles is significantly reduced for TiNiHf films bound to a SiO2/Si substrate compared to the functional fatigue DSC results reported for freestanding films. The thermal hysteresis width is also reduced for TiNiHf films constrained by SiO2/Si and Si substrates compared to freestanding films of similar thicknesses. With proper composition selection and microstructural control, TiNiHf films can be promising SMA films for bistable actuators with PMMA/TiNiHf/Si composites.