Study On Microstructures And Magnetostrictive Properties In Fe-Ga Alloys

Fe-Ga alloys attract much attention as magnetostrictive materials due to their excellent performances,such as a low saturation field?Hs?,a relative large saturation magnetostriction??s?,and good mechanical properties.According to the relation between magnetostriction and Ga concentration in Fe-Ga alloys,two Fe Ga alloys with chemical compositions of Fe₈₂Ga₁₈ and Fe₇₄Ga₂₆ are intensively investigated including microstructure,mechanical behavior and magnetostrictive property.Three kinds of prepare methods are used to control the microstructure of FeGa alloys,such as mold-casting,spray-casting and hot-rolling.The Fe Ga alloys which are prepared by the three methods show bcc-Fe crystal structure at room temperature.The grain size of the mold-cast and spray-cast Fe₈₂Ga₁₈ alloys are around 200?m.The grain size of the hot-rolled one is around 300?m.The saturation magnetostrictions of Fe₈₂Ga₁₈ alloys are 32,41 and67ppm for the mold-cast,spray-cast and hot-rolled one,respectively.The grain size is about 150?m for the mold-cast and spray-cast Fe₇₄Ga₂₆ alloys.The saturation magnetostriction of Fe₇₄Ga₂₆ alloys are 55 and 41ppm for the mold-cast and spray-cast ones,respectively.Uniaxial-compressive deformation can intensively affect the microstructure and magnetostriction in Fe-Ga alloys.Deformation twinning appeares in FeGa alloys under the compressive deformation of 2%,5%and 10%,which is confirmed by the optical metallography and EBSD techniques.The twinning density increases with the increase of the amount of deformation.The saturation magnetostriction of the mold-cast Fe₈₂Ga₁₈alloys is 45,31 and 21ppm for the sample with pre-deformation of 2%,5%and 10%,respectively.The saturation magnetostriction of the hot-rolled Fe₈₂Ga₁₈ alloys shows similar behavior,which decreases from 67 to 48 ppm with the pre-deformation increased to3%.Moreover,the saturation magnetostriction of the mold-cast Fe₇₄Ga₂₆ alloys also decreases with the increase of the amount of deformation.The decrease of magnetostriction in the pre-deformed Fe₇₄Ga₂₆ alloys is attributed to the generation ofresidual stress and twin boundary in the sample,which may restrict the motion of magnetic domains under the applied magnetic field.The liquid nitrogen cryogenic-treatmentcan intensively affect themagnetostriction in Fe-Ga alloys.The saturation magnetostrictionin Fe₈₂Ga₁₈ and Fe₇₄Ga₂₆ alloys shows different behaviors.The saturation magnetostriction in the spray-cast Fe₈₂Ga₁₈ alloy increases from 36 to 55 ppm when the sample is cryogenic-treated several cyclses?1,10,30,70,and 90 cycles?,whereas the saturation magnetostriction in the spray-cast Fe₇₄Ga₂₆alloy decreases from 46 to 31 ppm.However,the cryogenic-treatment has little effect on the magnetostriction in Fe₈₂Ga₁₈ single crystal.The influnce of cryogenic-treatment to the magnetostriction in Fe Ga alloys may be related to the grain boundary effect.