Abstract
Strengthening η texture (⟨001⟩//rolling direction) through secondary recrystallization can significantly improve the magnetostriction coefficient of Fe-Ga thin sheets and expand the use of Fe-Ga alloys in high-frequency applications. However, the secondary recrystallization of Goss texture in Fe-Ga thin sheets deteriorates significantly with the thinning of the sheet thickness under the current inhibitors of micron-sized NbC particles or precipitates. In this paper, a new composite inhibitor system, composed of nano-sized MnS and Nb(C,N) precipitates, is proposed to induce the secondary recrystallization Goss texture in Fe-Ga thin sheets with thicknesses less than 0.3 mm. The density and size of MnS and Nb(C,N) is designed based on the effect of alloy composition and hot rolling parameters on the precipitation kinetics of MnS and Nb(C,N), including the relative nucleation rate-temperature (NrT) and precipitation-time-temperature (PTT) curves. It is found that the stored deformation energy increases the maximum nucleation rate and the fastest precipitation temperature. A large number of lamellar and rectangular precipitates (MnS and Nb(C,N)) with a size of 5∼20 nm were precipitated after hot-rolling at a temperature of 800∼1,050 °C and a total thickness reduction of 80%. These nano-sized inhibitors provide a strong pinning effect for the primary recrystallized grains, and induce abnormal grain growth of Goss grains at an annealing temperature of 950∼1,050 °C. Resultingly, centimeter-sized Goss grains with a small deviation angle and maximum magnetostriction coefficient of 264 ppm are successfully achieved in Fe-Ga alloy thin sheets with a thickness of 0.25 mm.
Highlights
Giant magnetostrictive Fe-Ga alloys, discovered in 2000, have attracted considerable attention due to the combination of large magnetostriction (3/2λ100 = 400ppm) in a low applied magnetic field (∼300 Oe) and excellent mechanical properties.1–5 The deviation angle between the ⟨100⟩ direction and the axial direction of the single crystal rod significantly affects the saturation magnetostriction coefficient
Centimetersized Goss grains with a smaller deviation angle and maximum magnetostriction coefficient of 264 ppm are successfully achieved in Fe-Ga alloy thin sheets with a thickness of 0.25 mm
The quantity and size of precipitates are regulated by the reasonable design of composition and rolling process parameters based on the effect of stored deformation energy on the thermodynamics and kinetics of precipitation
Summary
The combination of micron-sized NbC particles and the change in surface energy from H2S gas or sulfur used during annealing is used to pin normal grain growth and induce secondary recrystallization in Fe-Ga alloys, yielding centimeter-sized Goss grains with a magnetostriction coefficient exceeding 250 ppm with thickness over 0.3 mm.. The core problem for improving secondary recrystallization texture and the magnetostriction coefficient in thinner FeGa sheet is the insufficient pinning force to normal grain growth from the micron-sized NbC particles.. Based on the relative nucleation rate-temperature (NrT) and precipitation-time-temperature (PTT) curves of MnS and Nb(C,N), a composite inhibitor system, consisting of nano-sized MnS and Nb(C,N) precipitates, is prepared by a reasonably designed composition, hot-rolling temperature and reduction percentage These nanosized precipitates provide effectively pinning for the normal growth of the primary grains and induce abnormal grain growth of Goss grains at an annealing temperature of 950∼1,050 ○C. Centimetersized Goss grains with a smaller deviation angle and maximum magnetostriction coefficient of 264 ppm are successfully achieved in Fe-Ga alloy thin sheets with a thickness of 0.25 mm
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