Fabrication and Characterization of Nitinol-Copper Shape Memory Alloy Bimorph Actuators

Abstract

This study aims to examine the effect of annealing conditions on nitinol (NiTi) characteristics and applies this knowledge to fabricate a NiTi-copper shape memory alloy bimorph actuator. The effect of the annealing conditions was investigated at various temperatures, i.e., 500, 600, and 650°C, for 30 min. With the characterizations using x-ray diffraction, energy dispersive spectroscopy, and differential scanning calorimetry techniques, the results showed that annealing temperatures at 600 and 650°C were able to appropriately form the crystalline structure of NiTi. However, at these high annealing temperatures, the oxide on a surface was unavoidable. In the fabrication of actuator, the annealing at 650°C for 30 min was chosen, and it was performed at two pre-stressing conditions, i.e., straight and curved molds. From static and dynamic response experiments, the results suggested that the annealing temperature significantly affected the deflection of the actuator. On the other hand, the effect of pre-stressing conditions was relatively small. Furthermore, the micro gripper consisting of two NiTi-copper bimorph actuators successfully demonstrated for the viability of small object manipulation as the gripper was able to grasp and hold a small plastic ball with its weight of around 0.5 mg.

Micromachined Shape-Memory-Alloy Microactuators and Their Application in Biomedical Devices

“…Normally, one end of the cantilever will be fixed while the other end will provide displacement upon heating or cooling depending on the SMA properties. Among the latest studies of this kind of actuator is one reported by Wongweerayoot et al [91]. In [91], a 5 μm thick NiTi thin film was deposited on a freestanding copper structure forming a bimorph microgripper.…”

“…Among the latest studies of this kind of actuator is one reported by Wongweerayoot et al [91]. In [91], a 5 μm thick NiTi thin film was deposited on a freestanding copper structure forming a bimorph microgripper. According to the report, the microgripper was able to grasp and hold a small plastic ball weighing around 0.5 mg ( Figure 5).…”

Effects of deposition and annealing conditions on the crystallisation of NiTi thin films by e‐beam evaporation

“…Over the years, shape memory alloy (SMA) have such attractive advantages compared to other actuation mechanisms such as high power density, large actuation force, large displacement range, low cost, resistance to corrosion, and biocompatibility [1]. This makes SMA the preferred material to fabricate microactuators in various specific applications [2, 3], such as microgrippers [4, 5], micropumps [6, 7], endovascular surgery [8, 9], and microrobots [10, 11]. However, SMA‐based actuators have often been described as having a slow response speed caused by the low cooling speed of SMA [12], which is seen as a major hindrance for the broad implementation.…”

Thermal, electrochemical and mechanical properties of shape memory alloy developed by a conventional processing route

“…A lot of research has been carried out on shape memory alloys recently. Among them, Wongweerayoot et al [2] prepared a NiTi-Cu shape memory alloy bimorph actuator and studied the effect of annealing conditions on nitinol found that Ringer solution proved itself to be most corrosive followed by SBF and HBSS. The corrosion potential also changes in a similar fashion.…”