On the microstructure and thermal stability of rapidly quenched Fe–B alloys in the intermediate composition range between the crystalline and amorphous states

Abstract

The structure and the thermal stability of the Fe0.89B0.11 rapidly quenched alloy have been investigated. Transmission Mössbauer measurements were carried out as a function of temperature in the range from 148 K to 513 K. Room temperature x-ray diffraction and transmission and conversion-electron Mössbauer experiments, as well as 4.2 K spin-echo nuclear magnetic resonance measurements, were also performed after some selected thermal treatments for one hour between 523 K and 1273 K. Based on these experiments it is suggested that the alloy is inhomogeneous at nanoscopic scale and consists of a fine dispersion of a defective boride phase with an o-Fe3B-like short-range order, embedded in an α-Fe matrix. This result gives support to the models which indicate phase separation in the amorphous phase with o-Fe3B short-range order prevailing in the hypereutectic iron concentration range. This phase was found to be less stable than the undefective one present in the less boron concentrated alloys. The transformation into the equilibrium phases, analyzed with an Arrhenius-type temperature dependence for the increase of the relative fraction of Fe2B, led to an activation energy Ea = 1.38 ± 0.68 eV/atom.

X-ray diffraction and Mössbauer spectroscopy studies of a mechanosynthesized Fe75B25 alloy

“…The second sextet may be attributed to the metastable t-Fe 2 B phase. The values of hyperfi ne interaction parameters agree well with literature data [6,7]. The signifi cant broadening of spectral lines ( 1,2,3 in Table 2) testifi es the fragmentation of the structure down to the nanometer level.…”

Mössbauer study of the magnetism and structure of amorphous and nanocrystalline Fe81−xNixZr7B12 (x=10–40) alloys

“…The CEMS spectra recorded for the xϭ10 and 20 samples annealed at T A ϭ570 and 620°C in addition to the bcc-Fe͑Ni͒ phase show a large volume fraction of tetragonal iron borate (Fe 2 B and Fe 3 B), 27,28 which dominate in the spectra ͓Figs. 2͑j͒ and 2͑k͔͒.…”

“…Identification of this phase from the Mössbauer data is difficult because the parameters given by various authors differ significantly. In some cases the Fe 23 B 6 phase is claimed to be paramagnetic ͑spectrum consists of a quadrupole doublet͒, 29 which seems rather unlikely, whereas in other cases this phase is magnetically ordered with hyperfine fields of about 28.8 and 23.8 T. 28 Since in our case the phase formed is most probably not a pure Fe 23 B 6 but rather (Fe 1Ϫy Ni y ) 23 B 6 , the spectral component related to this phase consists of a broad sextet which may show up in the hyperfine field distribution as a peak at about 28 T. We observed such a case for the spectrum of the x ϭ40 sample annealed at T A ϭ582°C ͑Fig. 7͒.…”