Date of Award

7-13-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Engineering Technology

First Advisor

abhijit bhattacharyya

Abstract

Metal alloys which go through a hysteric transformation due to external stimuli such as thermal and/or mechanical fields are called shape memory alloys (SMA). Thin films of SMAs have many remarkable features and have been used in the fabrication of microactuators. One potential application is a SMA thin film based information storage device. In all these applications, the existence of the strong thermomechanical coupling inherent in the phase transformation is seen. Due to coupling, knowledge of not only the mechanical field but also the thermal field is essential. The objective of this work is to study the thermal behavior of the SMA by analyzing an infinitely extended SMA thin film, an isolated square island and periodic square island structures. The thermal characteristics of the thin film are presented not only for such geometries but also for different microstructures. The thermal response of these structures is analyzed during heating and further during a rapid cycle of heating and cooling in order to capture the time dependent behavior of a potential SMA memory device. In addition, a “Dual Phase Model” which considers the delay in the propagation of the heat flux and temperature gradient is adapted for ultra thin SMA films and/or very short heating & cooling times. In particular, the thermal problem of an infinitely extended thin film is studied for an SMA & compared to the results obtained with the classical Fourier’s law of heat diffusion. Finally, as a first step towards fabrication & characterization of SMA thin films, temperature dependent x-ray diffraction is used to study the evolution of phase during heating & cooling of a SMA thin film.

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