Dynamic actuation properties of TiNi shape memory diaphragm

In order to realize a micropump with a shape memory alloy (SMA) diaphragm actuator, TiNi thin film of about 7 mu m in thickness was deposited by flash evaporation and its dynamic deformation-shape recovery properties were studied using a bulge test. The TiNi diaphragm was deformed by applying a gas pressure of 200 kPa heated resistively to recover its initial flat shape, and then air-cooled to achieve deformation once again. During this thermal cycle, temperature and deflection of the diaphragm were monitored at its center. In order to monitor temperature, we fabricated a Cu-Ni micro thermocouple on the diaphragm by conventional evaporation. When the diaphragm was heated, shape recovery occurred at about 60 degrees C. This continued after the temperature for termination of reverse martensitic transformation, Af (about 70 degrees C), had been reached. Moreover, when the diaphragm was air-cooled, redeformation began even at temperatures higher than that for the commencement of martensitic transformation, Ms (about 60 degrees C). From a FEM simulation and temperature measurements taken using thermography, these results could be explained by the temperature gradient formed in the diaphragm due to thermal conduction. When heating rate was increased, time required to complete shape recovery decreased and maximum displacement for shape recovery increased. This could also be explained in terms of the temperature gradient. (C) 2000 Elsevier Science S.A. All rights reserved.