HIGH SATURATION MAGNETIZATION AND SOFT MAGNETIC-PROPERTIES OF BCC FE-ZR-B AND FE-ZR-B-M (M = TRANSITION-METAL) ALLOYS WITH NANOSCALE GRAIN-SIZE

A mostly single bcc phase with nanoscale grain sizes of 10 to 20 nm was found to form by annealing amorphous Fe-Zr-B, Fe-Zr-B-Cu and Fe-Zr-B-Cu-M (M = Hf, Nb or Ta) alloys for 3.6 ks in the range of 750 to 900 K. The composition range of the bcc phase extends from 5 to 7%Zr and 1 to 8% B for the Fe-Zr-B system and 5 to 8%Zr and 1 to 16%B for the Fe-Zr-B-1%Cu system. The bcc alloys exhibit high permeability (mu-e) above 10000 at 1 kHz combined with high saturation magnetization (B(s)) above 1.5 T and the highest values reach 14000 and 1.70 T for Fe91Zr-B2 and 20000 and 1.55 T for Fe87Zr7B5Cu1. The addition of 1 at% Cu causes an enhancement of mu-e through the decrease of the bcc grain size from 20 to 10 nm, in addition to an extension of the formation range of the bcc phase. It should be noted that the highest B(s) value is almost comparable to that for Fe-6.5 mass% Si and considerably higher than those of other practical soft magnetic materials while the mu-e values are much higher than for the Fe-Si alloy. Accordingly, the combined characteristics of high B(s) and mu-e values for the bcc Fe-Zr-B base alloys allow us to expect a subsequent development as a novel soft magnetic material.