Effects of volume fraction between single crystal Ni-Mn-Ga ferromagnetic shape memory alloy and silicone rubber on the martensite variant reorientation

Owing to the rapid development of future technologies, IoT, actuators, and sensors inside robots have attracted much attention. Among the actuator materials, ferromagnetic shape memory alloys (FSMA), whose shape change could be manipulated by controlling its temperature, stress, and/or magnetic-field, are considered to be appropriate actuator materials. Besides, FSMA further possesses high work/volume ratio and fast response further allowing it a promising actuator material. Polycrystalline and single crystalline Ni-Mn-Ga alloys were successfully fabricated by arc-melting and floating-zone methods, respectively. Phase constituents of the Ni-Mn-Ga alloys were verified to be the single 5-modulated (5M) martensite phase, whose martensite variant reorientation (MVR) could be triggered by either applying an external magnetic field or a stress field. An in- situ observation of the martensitic transformation from 373 K to 273 K was clearly revealed. The MVR of the Ni-Mn-Ga alloy driven by an external magnetic field was also confirmed. Besides, typical stress plateau was discerned while a compressive stress was applied to the Ni-Mn-Ga alloy. Effects of ratios of the Ni-Mn-Ga alloy to the silicone rubber showed a good correlation and has been well-explained. Furthermore, it was found that a threshold range of approximately 7 vol.%−13 vol.% of the Ni-Mn-Ga alloy is the lowest requirement for the commencement of MVR.