Bi-doping engineering of Ni-Mn-Ga polycrystals and resulting grain particles for smart Ni-Mn-Ga/polymer composites

Abstract

Actuators and sensors are core components in the modern devices and techniques, such as internet of things (IoT) and robots. Ferromagnetic shape memory alloys (FSMAs), particularly prototype Ni-Mn-Ga Heusler compounds, exhibiting giant periodic strains in response to the alternating magnetic field, are promising materials for such components. In the present work, a Bi-doping effect on the grain structure of the Ni-Mn-Ga polycrystalline alloy and properties of the grain particles obtained by a mechanical crushing using a well-controlled technique were studied in detail. Phase constituents, surface morphologies, chemical composition analysis, grain size distributions, thermal behaviors, and interfacial properties of the size-controlled Ni-Mn-Ga-xBi (x = 0.00–0.05 at.%) single crystalline (SC) particles have been investigated. Furthermore, a 20 vol.% of the optimized Ni-Mn-Ga-0.03Bi SC particles were regularly distributed within a silicone polymer. The resultant composite was elastically compressed up to 50% producing a large and recoverable deformation of the embedded individual particles, that was in-situ measured by an X-ray microcomputed tomography (μCT) 3-dimensional (3D) imaging. The observed variations in the strain behavior of particles were attributed to the difference in their martensitic phase states and their concentration in composite. The results are important for a design of Ni-Mn-Ga/polymer composites for vibration damping, magnetostrain actuators, and haptic applications.