Effect of Fe-B-Si composition on maximum thickness for casting amorphous metals

The maximum melt spun thickness which can be made amorphous was measured for Fe-B-Si compositions by determining the minimum in the coercivity vs. thickness curve. The peak value of this critical thickness, tc, was 42 μm, corresponding to the alloy Fe74B16Si10. This value is six times smaller than those previously reported. This difference is attributed to the more sensitive Hcmethod used to detect tcin the present investigation compared to the visual observation of crystals at 100X magnification used in the previous work. X-ray diffraction and differential scanning calorimetry were used to confirm that the minimum Hccorresponds to tc. The Hcvaried inversely with tcas expected from a model based on domain wall pinning on the surfaces. Changing the wheel material from Cu to steel, or decreasing the wheel diameter both increased tcbecause of better wetting of the wheel by the melt. Theoretical prediction of tc, based on theories of crystal nucleation and growth kinetics and on experimental studies of heat flow in the melt spinning process, gave Values of tcroughly comparable to those observed experimentally. The calculated peak in tcat Fe73B16Si11is close to the experimentally measured peak at Fe74B16Si10.