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 Fe91-xZr7B2Alx, Fe90-xZr7B3Alx, Fe91-xZr7B2Six, Fe90-xZr7B3Six, Fe91-x-yZr7B2AlxSiy and Fe90-x-yZr7B3AlxSiy alloys. These amorphous alloys crystallize through two stages of Am-->bcc-Fe+Am-->alpha-Fe+Fe3B. 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 Fe88Zr7B3Al2 and Fe86Zr7B3Si4 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 bce structure in the wide temperature range. The magnetostriction (lambda(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 (mu(e)) shows a maximum value at the composition where the zero lambda(s) is obtained and the highest mu(e) at 1 kHz and saturation magnetization (B-s) are 1.6 x 10(4) and 1.61 T, respectively, for Fe89Zr7B2Al2, 1.4 x 10(4) and 1.56 T, respectively, for Fe87Zr7B2Si4 and 1.2 x 10(4) and 1.55 T, respectively, for Fe88Zr7B2Si2Al1. The annealing temperature (T-a) range where the characteristics of lambda(s) similar to 0, mu(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 lambda(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 lambda(s), high mu(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.