Excellent high-temperature magnetic softness for Si-rich Fe-based nanocrystalline alloy with a small amount of Al

Finemet alloys exhibit superior soft magnetic properties with high initial permeability (μ), low coercivity and low core loss, which attracted a great deal of attention [1]. However, their application is limited to the temperature close to the Curie point of an amorphous matrix, T c am, because the intergranular magnetic coupling is usually interrupted by the paramagnetic amorphous matrix. As the result, FINEMET-type alloys as an example, are usually used at temperature not higher than 230°C [2], otherwise their coercivity and core losses are very high, and the available induction is too low. To overcome the limitation at elevated temperature of the existing Fe-based alloys, FeCo-based nanocrystalline alloys [3-6] were developed aiming for extending the soft magnetic character of nanocrystalline alloys to higher temperatures. However, the substitution of Fe by Co in Finemet alloys would result in the decreasing of initial permeability because of the increasing saturation magnetostriction [5]. Recently, the research concerning Si-rich Fe-based nanocrystalline alloy has opened a new field on the optimization of the soft magnetic properties at elevated temperature [7], but room-temperature magnetic softness was somewhat decreased by increasing Si content. It has been reported that dual phase nanocrystalline alloys with larger crystalline volume fraction or thinner intergranular amorphous layer, which usually exhibit excellent high-temperature magnetic softness, can be obtained in Si-rich Fe-based nanocrystalline alloys [8-10]. Furthermore, the substitution of Fe by Al in Finemet alloys could exhibit lower H and a higher permeability due to a reduction in K 1 [11,12], therefore, we partially substituted Al for Fe in Si-rich Fe-based nanocrystalline alloy and prepared Fe 72.9 Al 0.6 Si 17.5 B 5 Cu 1 Nb 3 , Fe 72.7 Al 0.8 Si 17.5 B 5 Cu 1 Nb 3 and Fe 72.5 Al- 1 Si 17.5 B 5 Cu 1 Nb 3 alloys to go on exploring their soft magnetic properties at high temperature. In order to estimate the high-temperature soft magnetic properties of Fe 72.9 Al 0.6 Si 17.5 B 5 Cu 1 Nb 3 , Fe 72.7 Al 0.8 Si 17.5 B 5 Cu 1 Nb 3 and Fe 72.5 Al 1 Si 17.5 B 5 Cu 1 Nb 3 alloys, we investigated μ.-T curves of the above nanocrystalline samples from room temperature up to 700°C and found that the optimum magnetic softness at high-temperature was obtained for Fe 72.7 Al 0.8 Si 17.5 B 5 Cu 1 Nb 3 alloy. Therefore, we majorly analysed the microstructure and the high-temperature magnetic softness of Fe 72.7 Al 0.8 Si 17.5 B 5 Cu 1 Nb 3 .