The Fabrication And Characterization Of Fe-Ga Magnetostrictive Alloys

Fe-Ga alloys show a low saturation mangentic field, a relative large magnetostriction and good mechanical properties superior to other magnetostrictive materials. The combination of these unique characteristics makes the alloys promising in the applications such as sensors and actuatior and the alloys have attracted more and more attantion. In this paper, the underlying relation between Ga concentration with phases, crystals structure, magnetostriction and mechanical properties of Fe100-xGax(14 ≤ x ≤ 31, at.%) alloys have been investigated by using synchrotron high-energy x-ray diffraction, metallographic observation, quasi-static mechanical test and magnetic-field indcued lattice-strain measurement. The present studies provide a fundamental understanding of Fe-Ga alloys, which will benefit the exploring of advanced thechnique to improve the functional behaviors of Fe-Ga alloys.The microstructure and crystal structure of Fe-Ga alloys are closely related to the chemical composition. In the spray-cast alloys, the phase transition sequence is single A2 phase to A2+D03 phase and single D03 phase to D03+B2 phase with the increase of Ga concentration. In the furnace cooled alloys, the phase transition sequence is A2 phase to A2+D03 phase and L12 phase to A2+D03 phase with the increase of Ga concentration. In the quenched alloys, the phase transition sequence is A2 phase to A2+D03 phase with the increase of Ga concentration. The D03 phase shows as black spot precipitates in the metallography.The temperature dependent mechanical measurements of the Fe-Ga alloys provide important information of the elastic modulus and compression strength for the designing of functional unit. The spray-cast alloys Fe-Ga alloys show a good plastisity even at-80 Celsius degree, where the serrated yielding phenomenon appears for the compostions of 16- 20 at%. Further studies show that the serrated yielding phenomenon is sensitive to the strain-rate. The mechanical properties of the furnace cooled and quenched Fe-Ga alloys are lowered in comparison with the spray-cast alloys, which is due to the abnormal grain growth during the heat treatment.The magnetostrictive performance of Fe-Ga alloys is close related to the crystal structure. The present results demonstrate that the single phase, either A2 or D03, exhibits a monotonic increase in the magnetostriction with increasing Ga concentration. The magnetostriction shows a decrease first and then an increase with the increase of Ga concentration from 18- 27 at%, which is realted to the ratio of A2 and D03 phases. The phase transition from D03 to B2 phases with the increase of Ga concentration from 27- 31 at% leads to the decrease of magnetostriction.