Processing and properties of Ni–Mn–Ga magnetic shape memory alloy based hybrid materials

Abstract

Magnetic shape memory (MSM) materials based on non-stoichiometric Ni–Mn–Ga (NMG) alloys have attracted extensive interest over the last decade because of their actuating, sensing, and damping properties. In addition to MSM phenomenon, NMG alloys have shown conventional shape memory effect, traditional and magnetic-field-assisted superelasticity, magnetocaloric, and special transport properties. The multifunctionality of MSM alloys may be utilized for actuators, sensors, dampers, and perhaps also for energy harvesting. The dominant mechanism behind the MSM phenomenon is the twin boundary movement in the martensitic phase, and in order to take the full advantage of above mentioned properties single crystals are usually desired. However, growth of Ni–Mn–Ga single crystals is quite tedious and high quality crystals are only limitedly available at a considerably high prize. Therefore, alternative material solutions based on hybrid concepts have attained increasing interest. NMG-polymer hybrids can be tailored for a particular application by a proper combination of NMG alloy and polymer and prepared in various forms including embedded NMG particles, ribbons, or sheets. These materials are especially interesting for applications in vibration damping, actuation, and sensing. Polymer selection is critical for the functionality of NMG-polymer hybrids, and the applied polymer should be selected based on the martensite type of the NMG alloy. E.g., the transition temperatures of both components should be adjusted carefully considering the application. The contact between NMG and polymer and the stiffness of the polymer are important. Excellent damping performance is obtained in the NMG-soft epoxy matrix below the martensite–austenite transition temperature region when compared to that of the pure polymer. The relative damping capacity is found to be better than that of any other known material.