Evolution of structural changes in nanocrystalline alloys with temperature
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Structural features of the NANOPERM-type alloys Fe91 − x Mo8Cu1B x with x = 12, 15, and 17 have been investigated by Mössbauer spectroscopy. The room-temperature Mössbauer spectra of the as-quenched alloys are characteristic of disordered structural arrangement, but traces of bcc-Fe(Mo) as well as a FeMo2B2 phase have been revealed by X-ray diffraction in all the samples. These results have been confirmed by conversion-electron Mössbauer spectroscopy. The differences between the opposite sides of the ribbon-shaped samples have been shown to stem from structural distinctions. From the point of view of hyperfine interactions, the x = 12 sample exhibits paramagnetic behavior. With increasing x, a contribution from ferromagnetic regions appears gradually, thus leading to an increase in the magnetic ordering temperature in the as-quenched state. Partially crystallized samples have been prepared by controlled annealing of the original precursors for one hour at temperatures ranging from 330 to 650°C in a vacuum. The temperature of the onset of crystallization has been determined to be of 430, 450, and 470°C for x = 12, 15, and 17, respectively. During the first step of crystallization, bcc-Fe(Mo) nanosized grains are formed. Surface features of the samples investigated have also been characterized by using atomic force microscopy.
PACS numbers76.80.+y 61.18.Fs 61.46.Hr
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