Effect of minor Co additions on the crystallization and magnetic properties of Fe(Co)NbBCu alloys

Abstract

The effect of partial replacement of Fe by Co (up to 8 %) on thermal stability, structure and magnetic properties of FeNbBCu alloys has been explored in this paper. The results indicate that Co reduces the stability against crystallization of the amorphous alloy and stabilizes the nanocrystalline phase prior to the further precipitation of metastable boride phases.Transmission Mössbauer spectroscopy reveals differences in the hyperfine interactions between the alloys: Co raises the mean hyperfine field of the amorphous state and differences in the nanocrystalline bcc-Fe(Co) environments between the alloys occur depending on the amount of Co near-neighbours in the bcc-Fe structure. The addition of Co has also a notable effect on the magnetic properties of both amorphous and nanocrystalline alloys increasing the Curie temperature, which shows a linear dependence with the Co composition, and the saturation polarization.

Magnetic properties of Fe–Co–Mo–Cu–B nanocrystalline ribbons with stressing surfaces

“…At the time, we have no indication for a new phase -other than bcc Fe-Co as reported by Conde et al [1]. Though it has been pointed out for very similar alloy system that Co promotes the crystallization of Fe borides [14], none were identified after an annealing below 600 • C. Thus we can suggest the observed Co-enrichment of the grains [11,14] as a preliminary explanation for the magnetic hardening, which rather diminishes the loop tilt.…”

Structural and Thermomagnetic Properties of Fe_{86-x}Zr_7M_xNb_2Cu_1B_4 (M~=~Co, Ni, (CoCr); x=0 or 6) Amorphous Alloys

“…As can be seen from Fig. 2 replacement of 6 at.% Fe by Co or Ni in Fe 86 Zr 7 Nb 2 Cu 1 B 4 alloy shifts the onset of crystallization towards lower temperature because of thermal stability reduction of amorphous phase [5]. On the contrary to Fe 80 Zr 7 Co 6 Nb 2 Cu 1 B 4 alloy the substitution of 3 at.% Co by Cr shifts the crystallization peak to the higher temperature because of amorphous structure stabilization [6].…”

Microstructure evolution and grain size distribution in nanocrystalline FeNbBCu from synchrotron XRD and TEM analysis

“…However, a kinetic model describing the crystallization process has not been yet established. Recent papers, have dealt with the transformation kinetics using KJMA kinetic equations obtaining abnormal values of Avrami exponent of n = 1 [21,25]. Such a low value is difficult to interpret in Avrami theory as some of the conditions are not fulfilled as random nucleation.…”

“…There is a significant slowdown in crystallization rate, usually observed in the primary crystallization of many HITPERM alloys [17,21]. This slowing down is expected due to the redistribution of the glass constituents to the intergranular amorphous phase causing concentration gradients at the interface of growing grains and acting as a diffusion barrier to further growth.…”