Preparation, Structure And Magnetostriction Of Rare Earth Doped Fe-Ga Alloy

Fe-Ga alloy, which is a new type of magnetostrictive material raised in recent years with high mechanical strength, good toughness, large low-field magnetostriction and low associated cost, is a good candidate for commercial application. However, the magnetostrictive properties of the practically prepared Fe-Ga alloys are quite small at present and less than one third that of Tb-Dy-Fe. Therefore, improvement of magnetostrictive properties of Fe-Ga alloy has attracted much attention of researchers in recent years. Based on the review of the present researches and some problems of Fe-Ga alloys, effects of rare earth doping, the content of doping, rapidly quenching and annealing on structure and magnetostriction of Fe83Ga17 were systemically investigated in this work. At the same time some significant results are given.Firstly, the effects of the rare earth Ce, Tb and Dy doping on the microstructures and the magnetostrictive properties of Fe83Ga17 alloy were investigated in this work. The results showed that Fe83Ga17 alloy is composed only of a single phase of A2 with bcc structure. Whereas rare earth element doped Fe83Ga17 alloys are composed of the A2 phase with bcc structure and a small amount of the secondary phase with significant magnetostrictive property. The secondary phase in light rare earth element doped Fe83Ga17 alloys is RFe2 phase, while the secondary phase in heavy rare earth element doped Fe83Ga17 alloys is RFe3 phase. Doping of rare earth element results in the preferred orientation along〈100〉of A2 phase of the Fe83Ga17R0.6( R=Ce, Tb and Dy) alloy. The microstructure of the Fe83Ga17 alloy presents the equiaxial morphology with coarse grains. However, the microstructure of the Fe83Ga17R0.6 alloy is a columnar structure with fine grains. The magnetostriction coefficient of the Fe83Ga17R0.6 alloy is significantly larger than that of Fe83Ga17 alloy. The improvement degree of magnetostrictive properties of Fe-Ga alloy varies with different rare earth elements doped in the alloy. The magnetostrictive property of Fe83Ga17Ce0.6 alloy is better than that of the Fe83Ga17Tb0.6 and Fe83Ga17 Dy0.6. And Fe83Ga17Ce0.6 exhibits the best magnetostrictive property among three alloys. And its maximum magnetostriction coefficient of 206×10-6 is obtained at the magnetic field of 557 k A/m.Secondly, the effects of the content of rare earth Ce doping on the microstructures and the magnetostrictive properties of Fe83Ga17 alloy were investigated. The results showed that the Fe83Ga17Cex(x=0.4, 0.6, 0.8 and1.0) alloys are composed of the A2 phase with bcc structure and a small amount of Ce Fe2 secondary phase except the alloy with x=0.2, which is composed only of a single phase of A2 with bcc structure. The micoscopic structures of Fe83Ga17 Cex alloys consist of the black matrix structure mixed with white network structure. The black matrix structure and white network structure are inferred as the A2 phase with bcc structure and Ce Fe2 phase, respectively. The magnetostriction coefficients of rare earth Ce element doped Fe83Ga17 alloys are larger than that of the Fe83Ga17 alloy except the Fe83Ga17Ce0.2 alloy. When x=0.8, the maximum magnetostriction coefficient of 356×10-6 is obtained at the magnetic field of 557 k A/m. For the Fe83Ga17 Cex alloys except the alloy with x=0.2, the noticeable increase of the magnetostriction coefficients derives from the formation of the secondary phase of Ce Fe2 phase and the preferred orientation along〈100〉of A2 phase of the Fe83Ga17 Cex alloy caused by doping of rare earth Ce.In order to further improve the magnetostrictive properties of the Fe83Ga17Ce0.8 alloys, the quenched Fe83Ga17Ce0.8 alloys were prepared by rapid solidification with different quenching rates. The effects and the mechanism of effects of rapidly quenching rate on the microstructures and the magnetostrictive properties of Fe83Ga17Ce0.8 alloy were investigated. The results showed that quenched Fe83Ga17Ce0.8 alloys are mainly composed of the A2 phase with bcc structure, a small amount of Ce Fe2 and unsymmetrical DO3 phase. The quenching rate restrains the formation of Ce Fe2 and unsymmetrical DO3 phase in the quenched Fe83Ga17Ce0.8 alloys. The micoscopic structures of quenched Fe83Ga17Ce0.8 alloys consist of the gray matrix structure, white bright dots and darker spots structure. The gray matrix structure, white bright dots and darker spots structure are inferred as the A2 phase with bcc structure, Ce Fe2 phase and unsymmetrical DO3 phase, respectively. With the increase of the magnetic field, the magnetostriction coefficients of quenched alloys increase. The absolute value of magnetostriction coefficient of alloy increases firstly and then decreases, finally recovered modestly with increasing quenching rate. The quenched Fe83Ga17Ce0.8 alloy with 6 m/s exhibits the best magnetostrictive property among all of alloys. And its maximum magnetostriction coefficient of 206×10-6 is obtained at the magnetic field of 557 k A/m. It is considered that the giant magnetostriction of rapidly quenched alloy with 6 m/s originates from the Ce Fe2 phase and unsymmetrical DO3 structure.Finally, the quenched Fe83Ga17Ce0.8 with 6 m/s was annealed at different temperatures. The effects of annealed temperature on the microstructures and the magnetostrictive properties of quenched Fe83Ga17Ce0.8 alloy were investigated. The results showed that annealed Fe83Ga17Ce0.8 alloys are also composed of the A2 phase with bcc structure, a small amount of Ce2Fe17 new phase and unsymmetrical DO3 phase. And the content of Ce2Fe17 new phase in the annealed Fe83Ga17Ce0.8 alloys at 1323 K is obviously more than that of other alloys. The annealed Fe83Ga17Ce0.8 alloys at 1323 K shows preferred orientation along〈100〉of A2 phase. The micoscopic structures of annealed Fe83Ga17Ce0.8 alloys consist of the gray matrix structure, white bright dots and darker spots structure. The gray matrix structure, white bright dots and darker spots structure are inferred as the A2 phase with bcc structure, Ce2Fe17 phase and unsymmetrical DO3 phase, respectively. With the increase of the annealed temperature, the absolute value of magnetostriction coefficients of annealed alloys decreases firstly and then increases obviously. The annealed Fe83Ga17Ce0.8 alloy at 1323 K exhibits the best magnetostrictive property among all of annealed alloys. And its maximum magnetostriction coefficient of 206×10-6 is obtained at the magnetic field of 398 k A/m. It is considered that the giant magnetostriction of annealed alloy at 1323 K originates from the preferred orientation along〈100〉of A2 phase and the relatively larger content of Ce2Fe17 phase in the alloy.