Characterization Research Of Two-phase Nanocrystalline (Fe_1-xCo_x)₈₆Hf₇B₆Cu₁ (x=0.05, X=0.3) Soft Magnetic Materials

Two-phase nanocrystalline alloys with low coercivities Hc, large saturation inductions Bs, large resistivities and good thermal stability are the newest generation of magnetically soft materials. In the present work, there are some misunderstandings about characterizing and investigating the microstructure of these soft magnetic materials, particularly about distinguishing structures of fine nanocrystals embedded in an amorphous from structures of total amorphous. X-ray diffraction (XRD), Electron diffraction (ED), and Mossbauer spectroscopy (MS) are three simple ways to characterize the amorphous phases and nanocrystalline phases. The aim of this paper is to investigate the microstructure of (Fe1-xCox) 86Hf7B6Cu1(x=0.05, x=0.3) alloy ribbons, and to estimate the ability, scope and apply conditions of XRD, ED, MS, trying to compare three ways of characterizing amorphous alloy and nanocrystals alloy, looking for a precise and convenient characterization way.Processes of this paper are as follows:The (Fe1-xCox)86Hf7B6Cu1(x=0.05, x=0.3) alloy ribbons were produced by single-roller melt-spinning technique. XRD, ED, MS were used for characterizing microstructures of as-quenched samples and distinguishing two-phase nanocrystalline alloy samples from total amorphous alloy samples. The average grain sizes of nanocrystals embedded in amorphous phases were determined from the XRD peak by using the Scherrer's formula. High-resolution transmission electron microscopy (HRTEM) image was applied to obtain the average grain sizes of nanocrystalline phase, which can not be observed by XRD.MS was used to measure crystalline fraction of as-quenched ribbons. The nanocrystallization was carried out by low frequency magnetic pulsing technique, and the structure of new sample was analyzed by XRD, ED, MS.Parameters of grain sizes and crystalline fraction are used to estimate apply scope, sensitivity and accuracy of characterizing from XRD, ED and MS. The conclusions are as follows:XRD measurements may not be able to verify the true microstructure; it can not distinguish two-phase nanocrystalline alloy samples from total amorphous alloy samples sometimes. The XRD patterns of grains with less than 8 nm reveal an amorphous halo. For the systems with nanocrystals more than 8 nm in size, embedded in an amorphous matrix, whether the identification sharper peak of the crystalline phases can be observed by XRD patterns depending on crystalline fraction.ED showed to be more sensitive than XRD in the detection of small size nanocrytalline grains or small crystal fractions. Electron diffraction patterns can be used to characterize microstructures of two-phase nanocrystalline alloys.Mossbauer spectra can be used to estimate crystalline fraction of alloys, but it can not give the visual information about grain sizes and distribution of nanocrystals embedded in amorphous phases.