Wide supercooled liquid region and soft magnetic properties of Fe56Co7Ni7Zr0-10Nb (or Ta)0-10B20 amorphous alloys

An amorphous phase with a wide supercooled liquid region before crystallization was formed in Fe56Co7Ni7Zr10-xMxB20 (M=Nb or Ta, x=0-10at. %) alloys by melt spinning. The glass transition temperature (T-g) and crystallization temperature (T-x) increase by the dissolution of 2% M and the degree of the increase is larger for T-x, leading to maximum Delta T-x( = T-x - T-g) of 85 K at 2% Nb and 87 K at 2% Ta which are larger by about 20 K than the largest value for newly developed Fe-(AI, Ga)-(P,C,B,Si) amorphous alloys. The crystallization of the Nb-containing alloys occurs through two stages of amorphous (Am)-->Am' + alpha-Fe+ gamma-Fe+Fe76Nb6B18 -->alpha-Fe + gamma-Fe + Fe76Nb6B18 + Fe2Zr in the range less than about 6% Nb and Am-->Am' + gamma-Fe-->gamma-Fe+Co3Nb2B5+Ni8Nb in the range above 8% Nb. The change in the crystallization process with Nb content seems to reflect the easy precipitation of gamma-Fe by the increase in the number of Fe-Nb pairs with weaker bonding nature as compared with the Fe-Zr pairs. The best soft magnetic properties were obtained at 2% Nb or 8% Ta. The saturation magnetization, coercive force, effective permeability at 1 kHz, and saturated magnetostriction in the annealed state for 300 s at 800 K are, respectively, 0.96 T, 2.0 A/m, 19 100, and 10 x 10(-6) for the 10% Zr alloy, 0.75 T, 1.1 A/m, 25 000, and 12 x 10(-6) for the 2% Nb alloy, and 0.85 T, 1.5 A/m 17 400, and 14 x 10(-6) for the 8% Ta alloy. The Curie temperature is 531 K for the 2% Nb alloy and 538 K for the 8% Ta alloy. The success in synthesizing the new amorphous alloys with the wide supercooled liquid region and good soft magnetic properties is promising for future development as soft magnetic bulk amorphous alloys. (C) 1998 American Institute of Physics.