WIDE SUPERCOOLED LIQUID REGION AND SOFT-MAGNETIC PROPERTIES OF FE56CO7NI7ZR0-10NB (OR TA)(0-10)B-20 AMORPHOUS-ALLOYS

An amorphous phase with a wide supercooled liquid region before crysta llization 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 D elta T-x( = T-x - T-g) of 85 K at 2% Nb and 87 K at 2% Ta which are la rger 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-contain ing alloys occurs through two stages of amorphous (Am)-->Am' + alpha-F e+ gamma-Fe+Fe76Nb6B18 -->alpha-Fe + gamma-Fe + Fe76Nb6B18 + Fe2Zr in the range less than about 6% Nb and Am-->Am' + gamma-Fe-->gamma-Fe+Co3 Nb2B5+Ni8Nb in the range above 8% Nb. The change in the crystallizatio n process with Nb content seems to reflect the easy precipitation of g amma-Fe by the increase in the number of Fe-Nb pairs with weaker bondi ng nature as compared with the Fe-Zr pairs. The best soft magnetic pro perties were obtained at 2% Nb or 8% Ta. The saturation magnetization, coercive force, effective permeability at 1 kHz, and saturated magnet ostriction 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 temperatu re is 531 K for the 2% Nb alloy and 538 K for the 8% Ta alloy. The suc cess in synthesizing the new amorphous alloys with the wide supercoole d liquid region and good soft magnetic properties is promising for fut ure development as soft magnetic bulk amorphous alloys. (C) 1998 Ameri can Institute of Physics.