Microstructure And Magnetostriction Of Directional Solidification Fe₈₂Ga_18-xAl_x（x=8.5,9.5） Alloys

Fe-Ga alloy was a new type of magnetostrictive material.It had higher magnetostriction compared to traditional magnetostrictive materials（Ni,Fe-Al）,and higher thermo-mechanical properties compared to rare earth-iron giant magnetostrictive materials（Tb-Dy-Fe）.It had great potential application value in transducer and micro displacement.On the basis of Fe-Ga alloy,Al was added to obtain the high electrical resistivity,high mechanical properties and low cost magnetostrictive materials,and the properties of the alloy were improved by annealing and magnetic field heat treatments.The microstructure of the Fe-Ga-Al samples was analyzed by means of optical microscope,X-ray diffraction and scanning electron microscope.The magnetostrictionwas tested by the multi-parameter magnetic testing system.The effect of magnetic field heat treatment on the magnetostriction of Fe₈₃Ga₁₇ waveguide wires was studied.The microstructure of large size directional solidification Fe₈₂Ga_18-xAl_x（x=8.5,9.5）rod alloy was A2 phase,doped with a small amount of lath DO₁₉ phase and punctate DO₃phase.The microstructurein all parts of rodwas not the same during the solidification process.At both ends of the outer surface the microstructure were A2 phase of more Ga and Al elements doped with lath DO₁₉ phase and punctate DO₃ phase.Magnetostrictionwas poor.LathDO₁₉ phase in subsurface disappeares and only the A2 phase doped witha small amount of punctate DO₃ phase was left.The magnetostrictionwas better in subsurface.The microstructure was A2 phase doped with lath DO₁₉ phase and punctate DO₃ phase in the coreandthemagnetostrictionwaspoor.ForFe₈₂Ga_9.5Al_8.5alloy,the magnetostrictionincreased from 108ppm to 169ppm after 600℃heat treatment and the magnetostriction increased from 169ppm to 182ppm after 200℃vertical magnetic field heat treatment.For Fe₈₂Ga_8.5Al_9.5 alloy,the magnetostriction increased from 89ppm to101ppm after 730℃heat treatment and the magnetostriction increased from 101ppm to122ppm after 200℃vertical magnetic field heat treatment.Both the compression and cooling could increase the saturation magnetostriction.Besides,cooling decreased the magnetostriction in low magnetic field and increased the saturation magnetic field.When the microstructure of the alloy was A2 phase doped with a small amount of point DO₃phase,the magnetostriction was the best.ForΦ0.5Fe₈₃Ga₁₇waveguide wire,300℃vertical magnetic field heat treatment could increase the saturation magnetostriction from 28ppm to 41ppm.ForΦ0.8 and1.0Fe₈₃Ga₁₇waveguide wire,200℃vertical magnetic field heat treatment could increase the saturation magnetostriction from 41/41ppm to 50/46ppmrespectively.The difference of magnetostriction of Fe83Ga17 waveguide wire with different sizes was not obvious after vertical magnetic field heat treatment.The signal of Fe83Ga17 waveguide wire become more obvious as the size gets smaller under the same magnetostriction.Therefore,Φ0.5Fe₈₃Ga₁₇waveguide wire was the best.It is found that the Fe-Ga-Al alloy with atom ratio of 82:9.5:8.5 had better magnetostriction in this research.The magnetostriction could reach 182ppm after600℃heat treatment and 200℃magnetic field heat treatment.In addition,the Fe₈₃Ga₁₇waveguide wire with the size ofΦ0.5 after 300℃vertical magnetic field heat treatment had better magnetostriction.