Investigation on thermomechanical behavior of CuAINi/polyimide bimorph

Abstract

Thin film deposition of various shape memory alloys (SMA) on different substrates using different deposition techniques is being studied to get two-way shape memory effect for micro-actuator applications. The ability of SMA to generate sufficiently large amount of forces, large strain recovery makes SMA a prime member for its use in micro-actuator applications. However, low actuation frequency of around 1Hz and low transformation temperature under 100 0C makes commercially used NiTi SMA unsuitable for its use in high temperature situations. The transformation temperature and frequency of actuation can be increased to some extent by the addition of Cu as a ternary element in NiTi SMA. As Cu-based SMAs are well known for its high transformation temperature and high frequency of actuation, CuAlNi SMA is selected for this research work. In this work, the thermo-mechanical behaviour of electrically actuated CuAlNi/Polyimide SMA bimorph has been studied in detail with three different compositions of SMA which was deposited using thermal evaporation technique. Thermomechanical behaviour is studied when actuation voltage, actuation frequency and applied load at bimorph was changed. Certain key relationships between these parameters are determined through experimental study. The life cycle behaviour of CuAlNi/Polyimide bimorph as well as Mn added CuAlNi/Polyimide bimorph is also studied. It is found from the experiments that Mn addition in CuAlNi significantly increases the actuation properties and life of CuAlNi thin film as a result of grain refinement and improvement in the ductility of CuAlNi. To study the compositional, morphological, thermal and mechanical properties of these CuAlNi SMAs relevant techniques and instruments have been used. All the results from these sophisticated instruments and the results of actuation prove the improvement in the thermal-mechanical properties of CuAlNi SMA thin film with addition of Mn.