Nanocrystallization process of the Fe69.5Cu1Nb3B9Si13.5Cr4 FINEMET-type alloy: an AFM study

Abstract

The different devitrification stages of Fe 69.5 Cu 1 Nb 3 B 9 Si 13.5 Cr 4 (F-Cr4) amorphous alloy were studied by atomic force microscopy (AFM) on samples annealed at 400, 600 and 670°C for different treatment times. The AFM images showed no topographic changes in the alloys treated at 400°C, indicating that only structural relaxations took place at this annealing temperature. Samples thermally treated at 600°C showed hemispherical features uniformly distributed on the surface, suggesting initiation of the nanocrystallization process. The nanocrystals formed had a size distribution of 15-40 nm, which is slightly affected by the annealing time. At 670°C the crystallization phenomena occurred with the formation of large crystals and an increase in roughness. The corrosion behaviour of the nanocrystalline alloys in 2 M HCl solution was correlated with the AFM studies. The potentiodynamic experiments for these alloys showed a significant decrease of the current density peak at the active-passive transition in relation to the F-Cr4 amorphous alloy. The results indicated that the corrosion resistance and passivating ability of the alloys are improved by the thermal treatment.

Change in Magnetic Anisotropy at the Surface and in the Bulk of FINEMET Induced by Swift Heavy Ion Irradiation

“…Niobium, with its large atomic radius, inhibits particle growth, and boron, as a non-metal, acts as an amorphizer in the system. Cu promotes the formation of nanocrystals [25,26]. By annealing FINEMET at 550 • C, which results in optimal soft magnetic properties, the microstructure is composed of DO3 type Fe-Si nanocrystals, surrounded by retained amorphous regions [26].…”

Influence of nickel content on the electrochemical behavior of Finemet type amorphous and nanocrystalline alloys

“…Both Cu and Nb play an important role in this process: Cu promotes nucleation of the a-Fe(Si) crystalline phase and Nb stabilizes the residual phase, decreasing the grain growth rate [1]. Furthermore, the chemical composition also determines the corrosion behavior of these alloys.…”

AFM investigations during the nanostructure formation in FeZrB alloys

“…3 for the line profiles corresponding to the amorphous and a partially crystallized samples). Probably, they could be as a consequence of some kind of rearrangement in the sample surface arising from the dc current annealing treatment, related to the initial growth of the nanocrystals [5][6][7]. The evolution of surface crystallization can be shown in the images corresponding to the JH ribbons at 250, 340 and 350 mA, where the development of nanocrystalline morphology is evidenced.…”

“…Hysteresis loops were measured for the magnetic characterization of the as-quenched and nanocrystalline samples. The IC-AFM study gives us information about the evolution of the sample surface during the formation of the Fe nanostructure [6,7]. The mean grain size of the nanocrystalline phase estimated from AFM images, are compared with respect to the corresponding one obtained by neutron powder diffraction patterns.…”