Annealing Effect on the Shape Memory Properties of Amorphous NiTi Thin Films

Thin film shape memory alloys have recently become a promising material for the actuation of devices on the microscale such as micropumps and microvalves. Their utilization, however, has been limited due to the difficulty in tailoring their properties for different applications. Control over the transformation temperatures as well as mechanical and shape memory properties is required to enable their widespread use. This study examines the effects of heat treatment time and temperature on the properties of amorphous, Ti-rich NiTi thin films on silicon substrates. The effects on the transformation temperatures are investigated through the use of temperature dependent optical microscopy and temperature dependent X-ray diffraction. The indentation modulus and hardness, as well as dissipated energy and depth recovery, are obtained through nanoindentation and atomic force microscopy. The role of microstructure and composition in altering both the mechanical and shape memory properties of the films is discussed.