Fabrication process and magnetostriction of terfenol-D/Epoxy composites for actuator applications

Abstract

Giant magnetostrictive Terfenol-D can be employed as actuator or transducer element under AC magnetic field up to approximately ~10 kHz, but at higher frequencies above 10 kHz, eddy current losses are known to restrict its applications. Magnetostrictive particulate composites have been developed to minimize the restrictions imposed by monolithic Terfenol-D, such as eddy current loss and brittleness since the 1970s. The disadvantages of these magnetostrictive composites are random crystal orientation and low magnetization and thus much lower magnetostriction. The first objective of this thesis is to develop the fabrication process of Terfenol-D/Epoxy composite, which can achieve the enhancement of magnetostriction as well as mechanical properties. It is necessary to know how the initial composition and annealing temperature can be affected on microstructure of Terfenol-D/Epoxy composite to obtain the optimum magnetostriction of Terfenol-D/Epoxy composite. The effect of the Tb/Dy, the RE/Fe ratio and annealing temperature on microstructure is thus investigated because these factors can significantly influenced on magnetostriction properties of Terfenol-D/Epoxy composite. The second objective is to analyze the effect of eutectic phase, residual stress caused by epoxy infiltration on magnetostriction and magnetic properties of Terfenol-D/Epoxy composite. Finally, modelling of magnetostriction of Terfenol-D/Epoxy composite is proposed based on a modified uniform strain assumption that considers the elastic modulus coupled in the preferred direction. The fabrication process of Terfenol-D/Epoxy composite consists of fabrication of as-grown Terfenol-D based on unidirectional solidification technique, reaction heat treatment and infiltration process. A directionally aligned cell structure of REFe2 phase in as-grown Terfenol-D is obtained by zone melting among unidirectional solidification method. During the reaction heat treatment of as-grown Terfenol-D, the eutectic...