Material design and shape memory properties of smart composites composed of polymer and ferromagnetic shape memory alloy particles

Ferromagnetic shape memory alloys (FSMAs) such as NiMnGa are expected to be new practical actuator materials with high driving frequency by magnetic field and large strain due to the shape memory effect (SME). However, the brittleness and poor workability of FSMAs, especially at a polycrystalline state, are serious problems and should be improved for a practical use. From this viewpoint a smart composite has been designed by a combination of a polymer matrix and FSMA particles (FSMAP), and a systematic investigation has been done for a NiMnGa-FSMAP/epoxy smart composite. This paper summarizes the design concept and some experimental results of the smart composite. It is pointed out that the single-crystal NiMnGa-FSMAP are easily made by mechanical crush due to the brittleness of FSMAs, and microstructural control is also possible by applying magnetic field during curing. Experimental study revealed that the NiMnGa-FSMAP/epoxy smart composites exhibit both tensile ductility and SME, and that shape memory properties become improved by decreasing particle size of FSMAP. It is concluded that the FSMAP/polymer smart composite has a large potential to be a new practical actuator material.