The influence of microalloying and heat treatment on the structure and properties of Galfenol with high gallium concentration

Abstract

The structure of soft-magnetic and magnetostrictive alloys of the Galfenol type Fe-(27-28) at.% Ga after various heat treatment regimes has been studied. The features of formation of both metastable and equilibrium ordered phases in alloys based on Fe-Ga and Fe-Ga-rare-earth elements have been examined. Alloys of these systems belong to the class of highly magnetostrictive materials (up to 400 ppm for monocrystals) used in electromagnetic drives and special sensors. Two-phase alloys with a nonequilibrium phase based on the bcc lattice (D03 structure) and the equilibrium phase based on the fcc lattice (L12 structure) are investigated. Isothermal annealing of the Fe3Ga alloy at 400°C was used to obtain a microstructure that allows analysis of the kinetics of phase transformations under well-controlled conditions. It is established that isothermal annealing entails the formation of a microstructure with a certain ratio of metastable bcc and equilibrium fcc phases having different magnetic properties. The kinetics and mechanisms of phase transformations in binary Fe-Ga alloys and in multicomponent Fe-Ga-Tb alloys are systematically studied using a complex of methods of physical material science (X-ray diffraction (XRD), scanning electron microscopy with EBSD analysis (SEM-EBSD), optical microscopy (LM), vibration magnetometer (VSM), mössbauer spectroscopy. The influence of microalloying of the alloys with terbium on structure and functional characteristics is discussed. The role of Tb in the stabilization of nonequilibrium phases at room temperature is shown. The influence of small additions (0.5 at.%) of Tb on the changes in the structure Fe-Ga alloys was studied by mössbauer spectroscopy.