Fabrication And Magnetostrictive Properties Of Fe-Ga-Al Alloy Rolled Sheets With Strong Goss Texture

Magnetostrictive materials can be used in transducers,actuators and guided wave inspection applications.When used in high-frequency electromagnetic environments,magnetostrictive alloys are usually rolled into thin sheets to reduce eddy current losses.As magnetostrictive properties of alloys are closely related to textures,the achievement of strong Goss textured sheets is help to maximize the magnetostriction along the rolling direction.It has indicated in Fe-Ga alloy rolled sheets that there are two possible means to obtain strong Goss textured sheets.One is the addition of inhibitors,which can control the grain growth during secondary recrystallization.However,Fe-Ga alloys have large grain boundariy embrittlement and are usually rolled at high temperature.It is hard to control the size of inhibitors in Fe-Ga alloys.At present,NbC particles as inhibitors in Fe-Ga alloy sheets are large(?m-sized)and have no strong enough inhibiting effect.Strong Goss textured sheets can not obtained only by the addition of inhibitors.The other one is the sulfur-induced surface energy effect,which can provide additional driving force for the growth of Goss grains.It is effective but has limitations due to the use of sulfur.In view of the problems of these two aspects,this paper is first to improve the ductility of alloys by Al alloying and thus control the rolling processes effectively.Fine NbC particles can be precipitated at proper temperature and have strong inhibiting effect.Therefore,the preferential growth of Goss grains can be achieved and the strong Goss textured sheets can be obtained by strongly inhibiting the growth of non-Goss grains.<001>oriented polycrystalline Fe82Ga18-xAlx(x=4.5,6,9,12,13.5)alloy rods were prepared by directional solidification technique.The maximum saturation magnetostriction of alloys approximately decreased as a linear function.But the maximum saturation magnetostriction of Fe82Ga4 5Al13.5 alloy was still up to 198 ppm.Compared with Fe-Ga alloys,Fe-Ga-Al alloys have much better ductility.The elongation of Fe-Ga and Fe-Ga-Al alloys is 1.3%and above 9.5%,respectively.At the range of 4.5-13.5 at.%Al,all of Fe-Ga-Al alloys have relatively large elongation at room temperature.But the large elongation of alloys with low Al content mainly results from twinning mechanism and that of alloys with high Al content mainly from slippling,leading to the better ductility at high temperature.The elongation of Fe82Ga4.5Al13.5 alloys can reach up to 121.3%during tensile tests at 650 ?.According to the kinetic and thermodynamic theory of second phase precipitation,the maximum nucleation rate temperature of NbC precipitation in(Fe82Ga4,5Al13.5)99.9(NbC)0.1 alloys was calculated under different nucleation mechanisms.It has indicated that the nucleation rate on dislocations is ten orders of magnitude larger than that of uniform nucleation.Therefore,nucleation on dislocations is the main mechanism for NbC precipitation.The temperature of maximum nucleation rate was calculated to be about 720 ?,within the range of which or below a near maximum nucleation rate can be obtained,resulting in the finest NbC precipitates.The microstructures,texture distributions and NbC precipitations were investigated in primarily recrystallized Fe-Ga-Al-NbC alloy sheets prepared by different rolling processes.It has shown that the primarily recrystallized sheets have significant influence on the achievement of Goss texture and high magnetostriction performance in the secondarily recrystallized sheets.Intermediate annealing is helpful to obtain dominant Goss,?-fiber and cube texture components in primarily recrystallized sheets.With the fine NbC inhibitors of 56?250 nm in size,strong Goss textured sheets can be obtained by continuous heating process at the heating rate of 0.25 ?/min without sulfur-induced surface energy effect.The maximum saturation magnetostriction of sheets can reach up to 156 ppm.After the optimization of rolling process,Fe-Ga-AI-NbC alloy sheets were fabricated by rolling processes consisting of hot rolling at 900 ?,warm rolling at 500 ?,low temperature intermediate annealing at 650 ? for 15 min and cold rolling.The primarily recrystallized sheets are dominated by ?-fiber and cube texture components.The size of NbC precipitates in primarily recrystallized sheets is about 45 nm.Strong Goss texture can be developed in sheets annealed by continuous heating process at the heating rate up to 2 ?/min or by isothermal annealing process at 1050 ? above 1 h without sulfur-induced surface energy effect.The maximum saturation magnetostriction of these two sheets can reach up to 170 ppm and 156 ppm,respectively.