Smart Shape Memory Actuator Based on Monocrystalline Ni 2 FeGa Glass-Coated Microwire

Shape memory alloys (SMAs) are a group of metallic alloys that recover to their original form after deformation. Shape memory effect (SME) is characterized by diffusion-less transition between two phases: austenite and martensite [1]. Up to date, the Heusler alloy with chemical composition Ni-Mn-Ga (near to stoichiometry 2:1:1) is one of the prototype of SMA [2]. This alloy is known for its large recoverable deformation up to 12% strain and high-frequency response (up to 1 kHz) induced by magnetic or mechanical loadings. However, in spite of its remarkable properties, Ni 2 MnGa has some drawbacks originating from the loss of Mn, relatively low Curie and martensitic transformation temperatures etc. [3]. Therefore, it is necessary to develop new alloy systems to overcome such a disadvantage. Alternatively, Ni 2 FeGa alloy have been proposed as promising magnetic shape memory alloy. Taylor-Ulitovsky method for production of glass-coated microwires allows easy production of few kilometres of high quality monocrystalline wire along entire length with well oriented crystallographic axis. It is shown that such wire is characterized by temperature induced shape memory effect accompanied by ~2% reversible strain. As a result of different anisotropy of both low- and high- temperature phase, such strain is accompanied by huge variation of permeability. In the given contribution we show how magnetic parameters must be adjusted in order to achieve up to 1600% change of permeability due to the phase transition. Such variation allows us to control straining very precisely, which transforms the microwires into the SMART shape memory actuators. This work was supported by APVV-16-0079.