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 thermal driven microactuators. The functional properties are demonstrated by means of a (Ti, Hf)Ni-Mo-PMMA composite

Entwicklung, Herstellung und Charakterisierung von Mikroaktoren mit Formgedaechtnisschichten auf der Basis von TiNi

The thesis describes the fabrication process of TiNi, Ti(Ni,Cu), Ti(Ni,Pd) and Ti(Ni,Pd,Cu) shape memory alloys by means of DC-magnetron sputtering, their characterization and the optimization of the process conditions according to the application of the films in microsystems. The transformation temperatures of free-standing shape memory films have been determined by differential scanning caliometry and the contained phases and structure by means of X-ray diffraction, wavelength dispersive X-ray analysis and transmission-electron microscopy. The investigated films show in principal the same transformation behavior as it is known from bulk material. However, the transformation temperatures depend strongly on the annealing temperature, that is necessary to crystallize the amorphous films after deposition. The reason for this behavior could be found in Ti-rich precipitates. The favored formation of these precipitates in comparison with the parent phase upon crystallization lowers the transformation temperatures significantly. The investigated free-standing shape memory films are already in use in valves. Especially the use of Ti(Ni,Pd) films is advantageous with respect to binary TiNi-films due to their high transformation temperatures. The main topic of this thesis is the characterization of composites consisting of the shape memory thin films and substrates of Mo, Fe_7_2Cr_1_8Ni_1_0_- and Si. For the temperature dependent measurement of the curvature of these composites a suitable device has been constructed. By means of this equipment changes of the hysteresis shape and hysteresis width depending on the stress state of the shape memory films could be detected. If the lower temperature limit of the measurement is chosen conveniently, the hysteresis width of Ti_5_1_._8Ni_3_2_._1Cu_1_6_._1 and Ti_5_1_._2Ni_3_9_._2Pd_9_._6 films vanishes completely. Furthermore, the thesis describes the fabrication of actuators that consist of different layers, including sacrificial layers and layers for electrical isolation of shape memory films and metallic substrates. The presented fabrication process is compatible to batch-process technology and since the films can be deposited on silicon, the process is also compatible to microelectronics. To ascertain the applicability of the investigated shape memory alloys, calculations to the work output and the dimension of the shape memory composites are presented and discussed. In comparison with bimorphs shape memory composites145 refs.Available from TIB Hannover: ZA 5141(6467) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman