Thermal and magnetic properties of Fe56Co7Ni7Zr10-xNbxB20 amorphous alloys with wide supercooled liquid range

Amorphous alloys with a wide supercooled liquid region of 45 to 85 K were found to be formed in Fe56Co7Ni7Zr10-xNbxB20 (x=0 to 10 at%) alloys by melt spinning. The glass transition temperature (T-g) and the crystallization temperature (T-x) increase by the dissolution of 2 to 4%Nb. The degree of increase is larger for T-x than T-g, leading to the maximum Delta(x)(=T-x-T-g) of 85 K for the 2%Nb alloy. The Delta T-x value is about 20 K larger than the largest value for the newly developed Fe-(Al, Ga)-(P, C, B, Si) amorphous alloys. The crystallization occurs through a single stage, amorphous-->alpha-Fe+gamma-Fe+Fe2Zr+Fe-76,Nb6B18, for the alloys containing less than about 6%Nb and through two stages, amorphous-->amorphous+gamma-Fe-->gamma-Fe+Co3Nb2B5+Ni8Nb, for the alloys containing more than 8%Nb. The change in the crystallization process for the Nb-rich alloys probably reflects the disappearance of Fe-2(Nb, Zr) precipitates because of the weaker bonding of Fe-Nb pair as compared with Fe-Zr one. As the Nb content increases, the saturation magnetization (I-s) and permeability (mu(e)) of the annealed alloys decrease while the coercive force (H-c) remains almost unchanged. The good soft magnetic properties are obtained for the alloys containing less than 2%Nb subjected to annealing for 300 s at 800 K and the I-s, H-c and mu(e) at 1 kHz are 0.96 T, 2.0 A/m and 19100, respectively, for the 0%Nb alloy and 0.75 T, 1.1 A/m and 25000, respectively, for the 2%Nb alloy. The success of synthesizing the new amorphous alloys with a wide supercooled liquid region more than 80 K and with good soft magnetic properties is promising for future development as soft magnetic bulk amorphous alloys.