Microstructure and Soft Magnetic Properties of Nanocrystalline Fe–Zr–B–Al, Fe–Zr–B–Si and Fe–Zr–B–Al–Si Alloys with Zero Magnetostriction

An amorphous phase was formed in the composition ranges of Al or Si up to 15 at% for rapidly solidified Fe 91-x Zr 7 B 2 Al x , Fe 90-x Zr 7 B 3 Al x , Fe 91-x Zr 7 B 2 Si x , Fe 90-x Zr 7 B 3 Si x , Fe 91-x-y Zr 7 B 2 Al x Si y and Fe 90-x-y Zr 7 B 3 Al x Si y alloys. These amorphous alloys crystallize through two stages of Am→bcc-Fe+Am→α-Fe+Fe 3 B. The first and second reaction temperatures are 773 to 923 K and 973 to 1073 K respectively. The annealing in the temperature range between the first and the second stages caused the formation of a nanoscale bcc structure in coexistence with the amorphous phase. The average particle size and interparticle spacing of the bcc phase in Fe 88 Zr 7 B 3 Al 2 and Fe 86 Zr 7 B 3 Si 4 alloys are about 15 nm and 10 nm, respectively, and the analytical compositions are 2 to 4 at%Zr and 3 at%Al or 6 at%Si for the bcc phase and 11 at%Zr and 1 at%Al or 3 at%Si for the remaining amorphous phase. The enrichment of Zr in the remaining amorphous phase causes the increase in the thermal stability of the amorphous phase which enables the formation of the nanoscale bcc structure in the wide temperature range. The magnetostriction (λ s ) value of the bcc Fe-Zr-B-Al, Fe-Zr-B-Si and Fe-Zr-B-Al-Si alloys as a function of Al and/or Si content changes from negative to positive value through zero around Fe-Zr-B-2%Al, Fe-Zr-B-4%Si and Fe-Zr-B-2%Si-1%Al. The permeability (μ e ) shows a maximum value at the composition where the zero λ s is obtained and the highest μ e at 1 kHz and saturation magnetization (B s ) are 1.6 x 10 4 and 1.61 T, respectively, for Fe 89 Zr 7 B 2 Al 2 , 1.4 x 10 4 and 1.56 T, respectively, for Fe 87 Zr 7 B 2 Si 4 and 1.2 x 10 4 and 1.55 T, respectively, for Fe 88 Zr 7 B 2 Si 2 Al 1 The annealing temperature (T a ) range where the characteristics of λ s ∼0, μ e > 10 4 and B s > 1.5 T are achieved is also extended from about 20 K for the Fe-Zr-B alloy to about 100 to 130 K for the 2 at%Al or 4 at%Si alloy. The zero λ s for the 2 at%Al or 4 at%Si alloy is related to the simultaneous dissolution of Zr and Al or Si in the nanoscale bcc phase. The simultaneous achievement of zero λ s high μ e and high B s in the wide T a range through the dissolution of more than two solute elements in the bcc phase and the redistribution of solute elements between the bcc and amorphous phases is important for future development of the present magnetic alloys.