Shape Memory Behavior of NiMnGa/Epoxy Smart Composites

摘要

A new type of smart composite developed in our group was studied in terms of shape memory behavior. The smart composites were composed of NiMnGa ferromagnetic shape memory alloy particles (FSMAP) and a polymer matrix, where NiMnGa FSMAP will bring shape memory effect and the matrix polymer enhances ductility. Two kinds of NiMnGa were selected by taking the phase constitution into account (parent or martensite state at room temperature). The shape memory properties are reported in terms of transformation temperature, powder size, applied stress and heating/cooling rate. It was found that martensitic transformation temperatures of the smart composites obtained by differential scanning calorimetry (DSC) were almost equal to those of NiMnGa FSMAPs. The shape recovery of the composites was confirmed in the strain-temperature curves obtained by dynamic mechanical analysis. Clear shape change was recognized corresponding to the martensitic transformation temperatures. The shape memory properties depend on heating/cooling rate, particle size and applied stress. Lower heating/cooling rate and smaller particle size brings better shape memory properties. This is because thermal conductivity of polymer is low and the amount of defects such as pores introduced during curing decreases with decreasing particle size. The improvement of processing is needed to reduce material defects.