Pecularities of nanocrystal formation in rapidly quenched (FeCo)MoCuB amorphous alloys

Abstract

SummaryThe effect of the substitution of Fe by Co on the enhancement of glass-forming ability limits and subsequent nanocrystallization was studied in a rapidly quenched amorphous system (Fe x Co y ) 79 Mo 8 Cu 1 B 12 for y/x ranging from 0 to 1. The effect of Cu on nanocrystallization was investigated by comparison with Cu-free amorphous Fe 80 Mo 8 B 12 . Systems partially crystallized at the surface layer were prepared for y/x = 0 using different quenching conditions. The effect of heat treatment of master alloys used for ribbon casting was also assessed. The microstructure and surface/bulk crystallization effects were analysed using transmission electron microscopy and electron and X-ray diffraction in relation to the expected enhancement of high-temperature soft magnetic properties, drastically reduced grain sizes (∼5 nm) and Co content. Unusual surface phenomena were observed, indicating the origin of possible nucleation sites for preferential crystallization in samples with low Co content.

Surface morphology in amorphous Fe–Mo–Cu–B ribbon system

“…4. The thickness of this crystalline layer is well below 1 micron, as shown by cross-section transmission electron microscopy [4]; its removal by polishing leads to amorphous X-ray traces. Top ribbon sides, however, indicate systematically the presence of amorphous phase only.…”

“…It seems that any surface effects related to partial crystallinity on either surface can be fingerprinted (if at all) only by methods with resolution directly related to the size of the quenched-in nanocrystalline phases; AFM seems a convenient instrument for such investigations in future, as indicated previously [1,5], alongside with transmission electron microscopy of both surfaces or in cross-sectional view. It is to be noted that the surface layer with occurrence of quenched-in crystallinity is quite thin, being of the order of $100 nm [4].…”

“…The correlation between crystalline phases present in the precursor master alloy and quenched-in crystallinity in as-cast ribbon was noted. Three different types of crystalline phases were observed: bcc-Fe(Co, Mo), tetragonal Fe 3 B and tetragonal Mo 2 B 2 Fe [1,4].…”

Preparation and Crystallization Kinetics of FeSiB Amorphous Ribbons under Non-Isothermal Regime

“…Smart characterization of magnetic materials is also critical for sensor design and development [6][7][8][9][10]. Structural characterization is the key element in sensing core material characterization [11][12][13][14][15][16]. Correlation of properties with structure is of decisive importance in sensing element design [17][18][19][20].…”

Characterization of Amorphous, Magnetic Fe-Si-B Ribbons

“…The capability of producing amorphous alloys increases when amorphizing elements such as boron and silicon are used in different compositions and form substitutional solid solutions with iron, chromium or nickel or chromium [10][11][12][13][14][15]. Though, it is well known that amorphous structure is a thermodynamically metastable state and can evolve to a stable state spontaneously or driven by an external energy such as stress, heat etc [16][17][18][19][20]. The aim of the present work is the study of the thermal stability and the magnetic properties analysis of the Febased amorphous alloys using Differential Scanning Calorimetry (DSC), Thermomagnetic Gravimetry (TMG), X-ray Diffraction (XRD) and, finally, Barkahausen Noise Measurements (BHN).…”