| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 106 === Amorphous Ti-rich TiNi SMAFs were deposited using magnetron sputtering. Only crystallized films have shape memory effect and superelasticity. In this study, a normal laser engraving machine, continuous CO2 laser, pulsed UV laser and pulsed IR laser were used to anneal shape memory thin films. However, due to the limitation of the apparatus, problems like nonuniformity, high reflectivity of laser, heat affected zone, severe oxidation and damage occurred when using normal laser engraving machine and continuous CO2 laser. When using pulsed UV laser, the thickness of crystallized region was only 400 nm which is hard to measure their superelasticity by nanoindentation. In IR laser, the relationship between laser annealing parameters and the mechanical properties was studied. The cross-section of annealed-film showed crystallized surface layer of 800 nm to 1 μm in thickness and other region remained amorphous. The reduced Young’s modulus, micro-hardness and superelastic behavior of laser-annealed SMAFs were characterized using nanoindentation. After laser annealing, the reduced Young’s modulus decreased from ~127 to ~86 GPa and hardness decreased from ~7 to ~5 GPa indicating the formation of austenite phase on the sample surface. For the films scanned (i.e., annealed) by the laser beam multiple times in the same region, the film could be burned when the scanning times exceeded a critical number. This critical number decreased as the laser power increased. Without burning the film, the stress required to induce martensitic transformation decreased slightly with scanning times, while the reduced Young’s modulus and hardness didn’t show obvious change. The mechanical properties for films scanned at different laser powers for the corresponding critical times were also studied. Both the reduced Young’s modulus and stress required to induce martensitic transformation decreased drastically as the parameters changed from low power/high scanning times to high power/low scanning times. This study also indicates that the ratio between scanning speed and line spacing should match to reach a better superelasticity. For laser annealing films at an elevated substrate temperature, phase transformation will become easier and the plastic deformation increase. The increasing of plastic deformation comes from the effect of oxidation. The present results would be helpful in selecting laser annealing parameters to crystalize amorphous TiNi-based SMAFs.
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