The effect of metallic elements on the crystallization behavior of amorphous Fe-Si-B alloys

The crystallization behavior of amorphous Fe_84-X Si₆B₁₀M_X (M=Nb, Zr, V, or Cu) alloys was examined using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) with the aim of clarifying the effect of additional M elements. The compositional dependence of the first crystallization temperatureT _x1 increased in the order of Zr > Nb > V; however, the addition of 1 at. pct Cu caused a decrease inT _x1. Such an effect of the M elements on the thermal stability of an amorphous phase was interpreted in terms of the difference in the atomic size. These alloys were composed of a mixed structure ofα-Fe and amorphous phases after aging for 3.6 ks in the first exothermic temperature range. The addition of more than 3 at. pct Nb or Zr significantly affected the morphology and grain size of theα-Fe phase. However, their particles possessed dendritic morphology with a grain size of 0.1 to 0.3 µm, when the Nb or Zr content was less than 2 at. pct. Further addition of these elements brought about the formation of sphericalα-Fe particles. The average grain size, for instance, was as small as 20 nm in the aged alloy containing 6 at. pct Nb, which shows that a remarkable grain refinement occurs with increasing Nb content.