Study On Directional Solidification Microstructure And Properties Of Tb-Fe Alloys Under High Magnetic Fields

Re-Fe-based magnetostrictive material has the advantages of large strain,high energy density,high energy conversion efficiency and it is an ideal material for realizing electricity-magnetic-mechanical energy conversion.The easy growth direction of Tb-Fe alloy is<100>and the direction of easy magnetization axis is<111>.Therefore,preparation of Tb-Fe alloy with<111>orientation is an effective way to improve its magnetostriction.In this paper,the Tb-Fe alloy with the highest magnetostrictive coefficient of saturation at room temperature was taken as the research object,the combination of strong magnetic field and directional solidification technique is used to study the orientation behavior of RFe3 and RFe2 under strong magnetic field and the relationship between them.Inspected the relationship between orientation of TbFe2 phase and microstructure and properties of the material during the directional solidification in a strong magnetic field.Based on mechanism of the effect of the strong magnetic field on the microstructure and properties of the material,preparation of Re-Fe-based magnetostrictive material with high<111>orientation and significant enhancement of magnetostriction by using strong magnetic field.The main findings are as follows:(1)There are three main phases in the directionally solidified Tb-Fe alloys:TbFe2 phase,TbFe3 phase and R-rich phase.The TbFe3 phase and the R-rich phase in the alloy all grow along the directional solidification direction.The change of solidification rate and magnetic field strength can not change the composition and distribution of Tb-Fe alloy phase.With the increase of solidification rate and magnetic field strength,the spacing between two phases of TbFe3 phase in Tb-Fe alloy decreases gradually.(2)The composition of cross-section of Tb-Fe alloy after directional solidification is consistent with longitudinal section,but the direction of the phase is irregularly arranged.With the increase of directional solidification rate,the microstructure of the longitudinal section of Tb-Fe alloy is refined.The crystal orientation of Tb-Fe alloy does not change with the increase of the solidification rate,but the crystal orientation of Tb-Fe alloy changes from<113>?<110>?<111>along with the increase of magnetic field intensity rotation of the magnetization axis.(3)With the increase of solidification rate and magnetic field intensity,the saturation magnetization of Tb-Fe alloy after directional solidification shows an increasing change.The magnetization rate also increases with the solidification rate.The magnetostriction coefficient of Tb-Fe alloy at 200 ?m/s and 50 ?m/s is higher than that at the solidification rate of 100 ?m/s.Under the same solidification rate,the magnetostriction coefficient of Tb-Fe alloy increases with the increase of the magnetic field strength.(4)The Tb-Fe alloy undergoes brittle fracture during the compression and occurs at the phase boundary.As the solidification rate increases,the compressive strength of the sample increases.With the increase of magnetic field strength,the compressive strength of samples decreases.