The secondary recrystallization texture and magnetostriction in Fe-Ga alloy ultra-thin sheet

Abstract

Fe-Ga alloy is an advanced magnetostrictive material for actuators and sensors in terms of combining excellent mechanical and magnetostrictive properties. It is desirable to produce η(<100>//RD) textured Fe-Ga sheets due to the magnetostriction anisotropy with the largest coefficient along <100> direction and the serious eddy current loss in high-frequency use 1,2. The secondary recrystallization Goss ({110}<001>) texture and large magnetostriction coefficient were mainly achieved in Fe-Ga aaloy thin sheet with the thickness of 0.3~0.5mm, by the combination of micron-sized NbC particles and surface energy effect in high-temperature annealing 3,4, as well as the initial sharp <100>-oriented columnar grains by directional solidification 5.Since the eddy current loss is proportional to the square of the sheet thickness, the thinning of the sheet thickness can improve the energy conversion efficiency significantly. However, the secondary recrystallization of Goss texture significantly deteriorated in the Fe-Ga alloy sheet with a thickness of less than 0.3 mm due to the insufficient pinning force from the micron-sized NbC particles 6. The introduction of surface energy effect from H2S or S element, as well as the initial columnar crystals by directional solidification 7, cannot guarantee the complete secondary recrystallization in Fe-Ga alloy sheet with the thickness less than 0.3 mm. Qi et al 8 supposed the 0.10-mm Fe-Ga alloy ultra-thin sheets were prepared by rolling the 0.3 mm secondary recrystallized sheets, the strong cube texture and magnetostriction of 140 ppm were obtained after annealed for 2 h at 1200 °C under a flowing argon–hydrogen mixture. However, the preparation process is complicated and the incomplete secondary recrystallization restricts the magnetostriction coefficient. Therefore, it is necessary for the realization of complete secondary recrystallization in the Fe-Ga alloy sheet with a thickness of less than 0.3 mm.In the present study, the Fe-Ga ultra-thin sheets with the thickness of 0.10–0.25 mm were prepared via two-stage cold rolling method. The composite inhibitors composed of nanometer-sized sulfide and carbonitride are dispersedly precipitated during hot rolling and subsequent annealing, which provides effective pinning force for the normal growth of matrix grains. The gradually dissipated inhibition force during high-temperature annealing promotes a few exact Goss grains to grow abnormally by consuming primary recrystallized matrix grains textured by γ-fiber. Centimeter-sized secondary recrystallization Goss grains and large magnetostriction coefficient as high as 240 ppm is obtained in Fe-Ga alloy ultra-thin sheet without surface energy effect. The result indicates that complete secondary recrystallization can be realized based on the precise design and control of nano-sized composite precipitates and primary recrystallization microstructure/texture in Fe-Ga alloy ultra-thin sheet by conventional rolling and annealing methods. **