Shape memory behavior, and internal structure of Ti-Ni-Cu shape memory alloy thin films and their application for microactuators

Internal structure and shape memory behavior of Ti-38.3Ni-9.3Cu (at%) thin films heat-treated at 873 K, 923 K. 973 K and 1023 K,ere investigated by TEM observation and thermal cycling tests under various constant stresses. The thin film heat-treated at 873 K contained two types of precipitates, i.e., fine platelets and Ti2Ni particles. The density of the platelets decreased with increasing heat-treatment temperature and annihilated completely when the heat-treatment temperature reached 973 K. The Ti2Ni precipitates increased in volume fraction with increasing heat-treatment temperature from 873 K to 923 K, then their volume fraction was almost kept constant above 923 K. The recoverable strain decreased and the M-s increased with increasing heat-treatment temperature from 873 K to 923 K. both the recoverable strain and the M-s became almost constant when the heat-treatment temperature was above 923 K. A diaphragm-type microactuator utilizing a Ti-38.0Ni-10.0Cu (at%) thin film was fabricated. The diaphragm was square with the width of 500 mu m. The actuation properties were investigated under conditions of both quasi-static and dynamic actuation. The M, and the transformation temperature hysteresis of the microactuator were determined to be 352 K and 6 K, respectively. The microactuator operated at a working frequency of 100 Hz. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.