Evaluation of shape memory behaviour of NiTi bi-layer composite
Mahmoud Nili-Ahmadabadi, University of Tehran, Tehran, IranMohammad Hassan Malekoshoaraie, University of Tehran, Tehran, Iran
NiTi alloys are attractive materials for a wide range of smart designs and innovative applications due to their fantastic functional properties, like shape memory effect and super elasticity. Recently the concept of creating multi-layer and composite NiTi alloys by joining of NiTi to itself and to other materials has been explored in order to meet distinctive applications and improve its properties. Most of the investigations on composite NiTi focus on NiTi-based films and few attention has been given to NiTi bulks while it could have much more applications in industries.
In this contribution, two NiTi layers with different composition, structure and thickness were bonded to each other by diffusion bonding method. The penetration at interface and microstructure of composite was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In order to elucidate compositing shape memory behaviour, tensile test with a uniaxial testing machine were carried out at room temperature.
Results indicate that a chemical composition gradient was formed in the interface zone after diffusion bonding, which was free of any metallurgical defect and with appropriate mechanical properties. Moreover, not only the shape memory behaviour improved in the bi-layer specimens, but also they showed two-way shape memory effect without any complex thermomechanical process. Such shape memory behaviour offers new options for innovative designs of NiTi, in particular actuators and bionics devices.