Composites of different shape memory alloys and polymers for complex actuator motions

By combining shape memory alloys with different hysteresis widths, complex actuator movements can be achieved. This contribution presents the properties of a combination of (Ti,Hf)Ni and Ti(Ni,Cu) films that enables the creation of an actuator with wave-like behavior. This wave-like behavior is convenient for walking and swimming microrobots. It can be initiated by simple heat pulses without the need for complex phase control. Deflection measurements of the corresponding cantilevers reveal the workability of such an actuator concept. The contribution also presents the development of a bistable shape memory composite consisting of a (Ti,Hf)Ni shape memory alloy layer, a metallic substrate and additional polymer layers. The polymer is able to fix the deflection state of the (Ti,Hf)Ni-Mo actuator below its glass transition temperature if the glass transition is within the hysteresis of the shape memory alloy. This bistability leads to a reduction of the power consumption which is advantageous for thermally driven microactuators. The functional properties are demonstrated by means of a (Ti,Hf)Ni-Mo-PMMA composite.