Effect of Annealing Temperature on the Mechanical Properties and the Spherical Indentation of NiTi Shape Memory Alloy
NiTi alloy is one of the so-called shape memory alloys (SMAs). Its shape memory effect is derived from the phase transformation controlled by the temperature. With the similar spherical indentation produced in the measurement of Brinell hardness, a surfac
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Abstract NiTi alloy is one of the so-called shape memory alloys (SMAs). Its shape memory effect is derived from the phase transformation controlled by the temperature. With the similar spherical indentation produced in the measurement of Brinell hardness, a surface topography accompanied with residual stress is obtained on the polished NiTi alloy. Following the usual controlled heating performed in the SMA, the indented surface can nearly return to its flat surface configuration as the NiTi alloy goes through the martensite to austenite transformation. This study firstly focused on how to implement the SMA material tensile test at different controlled temperatures. Thus, the associated mechanical properties at different temperatures were obtained, and the effect of annealing temperature on the SMA’s phase transformation was also investigated. The thus formed spherical indentations on shape memory alloys could have reversible depth change, i.e., deeper depth in the martensitic phase at low temperature and shallower depth in the austenitic phase at high temperature. Thus, by controlling the temperature of the NiTi alloy, a surface with tunable morphology was demonstrated. Keywords Shape memory alloy • Superelasticity • Tunable surface morphology
T.-H. Tan • C.-Y. Lee (*) Department of Mechanical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan e-mail: [email protected] M.-w. Wu Chienkuo Technological University, Changhua 50015, Taiwan J. Juang and Y.-C. Huang (eds.), Intelligent Technologies and Engineering Systems, Lecture Notes in Electrical Engineering 234, DOI 10.1007/978-1-4614-6747-2_88, # Springer Science+Business Media New York 2013
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1 Introduction Due to the potential demand on the miniaturization and integration of biochips and other microchips for chemical analysis, the research in the microfluidic devices has been a popular topic recently [1]. The reduction of chip size down to 1 mm or less than 500 μm minimizes not only the required sample volume and testing time but also the operation cost. However, the effectiveness and accuracy of the test depends mostly on the fluidity and proper mixing of the reagent and sample inside microchannel. The low Reynolds number and diffusivity of fluid, worse for fluid with high molecular weight, poses a serious challenge on the device design. Among the different designs for the micromixers, they are categorized into active and passive devices. The active micromixer utilizes actuating forces, such as pressure, electrophoresis, or electric osmosis, to actuate the mixing. On the other hand, the passive design uses the geometrical shape of the microchannel to increase the interface interaction between two fluids [2–4]. Although the passive devices are simple to use and consume less energy, the controllability and mixing enhancement are not as effective as its active counterparts. Nevertheless, the complexity and high cost are the tradeoffs for using active devices. The tuning of the surface profile of the microchannel
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