AFM and Mössbauer spectrometry investigation of the nanocrystallization process in Fe–Mo–Cu–B rapidly quenched alloy

Abstract

In this paper, the effect of heat treatment on the development of nanocrystallites in rapidly quenched Fe79Mo8Cu1B12 alloy is investigated. The surface morphology is examined using non-contact mode atomic force microscopy (AFM). The results are compared with those obtained by transmission Mössbauer spectroscopy (TMS), conversion electron Mössbauer spectrometry (CEMS) and x-ray diffraction (XRD). It was found that the sample is not fully amorphous even in the as-quenched state. Minor amounts of bcc-Fe grains were detected on the wheel side of the ribbon-shaped samples while no indications of the crystalline phase were observed in the bulk. The crystallization onset is observed after annealing at 410 °C, when bcc-Fe nanograins are quite well developed. More intense crystallization is evidenced after annealing at higher temperatures, when the content of the crystalline phase increases progressively. The second crystallization, not discussed in the present paper, is characterized by the occurrence of additional crystalline phases, and appears after annealing at 650 °C. We suggest a crystallization model assuming no drastic change in the size of the primarily formed bcc-Fe nanograins with temperature as proved by XRD. The increase in annealing temperature induces the formation of a higher number of crystalline particles, which form large irregular agglomerates (80–130 nm in height), in accordance with the AFM data.

Surface Features of Nanocrystalline Alloys

“…Consequently, even though the degree of quenched-in nucleation centres at the air side is effectively lower its smooth surface favours the progress of crystallization via Ostwald ripening. [11] Finally, when the annealing temperature reaches 550 °C, which is well beyond the onset of bulk crystallization Tx1 (~ 445 °C), [12] all CEMS and CXMS spectra recorded from both sides of the 57 Fe81Mo8Cu1B10 MG ribbons look very alike in Figure 5 and Figure 6, respectively. The content of bcc-Fe nanograins is very similar and relatively high (> 60 %) though in the CEMS spectra (Figure 5b) their contribution is slightly higher at the air side than at the wheel side.…”

Mössbauer Spectrometry in FeMoCuB-Type Nanocrystalline Alloys

“…After annealing, sharp spectral lines appear that indicate a presence of crystalline phases. In the first stage of crystallization, they correspond to bcc-Fe phase with minute inclusions of Mo [4]. Again, depending on the composition of the master alloy, the crystallization starts at different temperatures of annealing.…”

Evolution of structure and local magnetic fields during crystallization of HITPERM glassy alloys studied by in situ diffraction and nuclear forward scattering of synchrotron radiation

“…DSR was performed at the KMC-2 experimental station at BESSY II, Berlin with the energy of 7 keV (λ = 0.177121 nm) and a photon flux of ~2x10 10 photons/s. The estimated heat load at the sample was 0.1 mW.…”

“…Mössbauer spectroscopy (MS) is a method that directly correlates magnetic states of the studied materials with their structure through hyperfine interactions [7][8][9][10]23]. It is, however, quite time consuming and thus not suitable for observation of rapid dynamic processes.…”