Research On Cu And Rare Earth Elements Doped Fe-Ga Magnetostrictive Materials

The Fe-Ga magnetostrictive alloys have attracted wide attention due to their advantages,such as higher magnetostriction under low applied magnetic field,low hysteresis,and well mechanical properties.At present,the researches on Fe-Ga alloys still have the following problems:1)The theoretical and experimental results of the influence of the non-magnetic transition group element Cu doping on the magnetostrictive properties of Fe-Ga alloys are inconsistence.And the way of Cu exisits in Fe-Ga alloys is unclear.2)The magnetostrictive mechanism of rare earth doped Fe-Ga alloys is not yet clear.About the magnetostrictive mechanism of rare earth doped Fe-Ga alloys is still not uniform.The origin of the magnetostrictive properties of rare earth doped Fe-Ga alloys is whether the distortion caused by the rare earth elements enter into A2 lattice or the formation of?001?oriented columnar crystals,which is still controversial.3)The research and development of flexible Fe-Ga magnetostrictive composite materials will be the focus of research in the field of Fe-Ga magnetostrictive materials at present and in the future.This thesis has conducted research on the above problems and got some meaningful conclusions:Firstly,this thesis investigates the microstructure and magnetostrictive properties of Cu doped Fe-Ga alloys.The investigations indicate that in(Fe₈₃Ga₁₇)_100-xCu_x?x=0,3,6,9,12,15?alloys,the x=0?6 at.%alloys are consist of single bcc structured A2 phase.While,the x=9?15 at.%alloys are consist of bcc structured A2 main phase and fcc structured FeCu₄ second phase.The doped Cu elements is dissolved into the A2 main phase lattice in the form of inerstitial doping,inducing the tetragonal-like distortion of A2lattice.In addition,Cu doping results in a decrease in the Young's modulus of the Fe-Ga alloy.With the increase of Cu content,the magnetoelastic couping coefficient of Fe-Ga alloy also decreases.Which results in the magnetostrictive coefficient of Fe-Ga alloy decrease with the increase of Cu content.Then,in the reasearches of microstructure and magnetostrictive properties of rare earth doped Fe-Ga as-cast alloys.It is found that in the Fe₈₃Ga₁₇Rx?R=La,Ce,Pr,Nd,Sm,Y,x=0,0.04,0.2?as-cast alloys,except for x=0 at.%alloy is consist of single bcc structure A2 phase,other alloys are consist of bcc strucutured A2 main phase and rare earth riched second phase.For Ce,Sm,Y doped Fe-Ga as-cast alloys,rare earth elements almost cannot enter into A2 lattice.In these alloys,the main factor what affects the magnetostriciton of Fe-Ga as-cast alloys is the content of?001?oriented columnar crystals.At the same time,the content of?001?oriented columnar crystals depends on the width of the supercooling zone(??4?at the front end of the liquid-solid interface during alloy solidification and the degree of supercooling of the composition.The wider width of the subcooling zone,resulting in the more favorable of columnar crystals formation.And the component subcooling in the front end of the liquid-solid interface,which will help to form a?001?orientation texture in the sample.For La,Pr,Nd doped Fe-Ga as-cast alloys,rare earth elements can enter into A2 lattice.In these alloys,rare earth elements enter the lattice expansion caused by the A2lattice,and the resulting residual strain or lattice distortion is the main factor affecting its magnetostriction coefficient.It is worth noting that the?001?oriented columnar crystals in these alloys will also improve the magnetostrictive properties of the alloy,but the real decisive factor is the residual strain and lattice distortion formed in the alloy.Finally,rare-earth Y and Pr doped Fe-Ga magnetostrictive composite materials were innovatively prepared,and their microstructure and magnetostrictive properties were studied.The study found that mixing the magnetostrictive powder,obtained after ball milling,with expoxy-binder and oriented it under applied magnetic field will cause the domains in the powder to rotate and align.While,the slip and rotation of grains will enhance the?001?preferred orientation of powder.These factors improve the magnetostriciton of the composite materials.Besides,compared with Y elements doping,due to the larger anisotropy of Pr element,magnetostrictive performance of Pr doped composite materials are better than Y doped counterpart.And the large mass ratio of the magnetostrictive powder to the epoxy binder is more conductive to the magnetostrictive performance of the composite materials.Excessive air-drying time is detrimental to the magnetostrictive properties of the composite materials.