Influence of microstructure on the magnetic and mechanical behaviour of amorphous and nanocrystalline FeNbB alloy

Abstract

The formation of a nanocrystalline structure and its influence on the magnetic and mechanical properties in a ternary Fe 80.5 Nb 7 B 12.5 alloy has been investigated using a variety of complementary methods. The crystallization studies performed by DSC calorimetry, magnetization and electrical resistivity measurements have confirmed a two-stage nature of the primary crystallization process. The microstructure in the series of heat-treated amorphous and nanocrystalline specimens with different volume fractions of crystalline phase was examined by transmission electron microscopy, x-ray diffraction and 57 Fe Mössbauer spectrometry. The results obtained by a combination of static magnetic measurements and Mössbauer spectrometry have indicated a higher degree of structural and magnetic inhomogeneity of the residual amorphous phase after nanocrystallization. Striking differences in the magnetic hardening regime at elevated temperatures have been observed for the samples with different volume fractions of nanocrystalline particles. The strongest magnetic hardening effects are visible for the samples exhibiting a medium degree of crystallinity, while the best soft-magnetic properties are obtained for the samples where the primary crystallization process is nearly finished. The ductility tests have revealed that the transition from ductile to brittle behaviour develops predominantly in an amorphous phase just before crystallization and the subsequent crystallization causes only slight changes in the embrittlement level. On the other hand, the hardness is rather insensitive to the structural relaxation processes before crystallization and its value increases proportionally to the volume fraction of precipitated nanocrystalline grains.

A magnetisation and Mössbauer study of triazole (M1−x2+Mx3+)M3+F5(Htaz)1−x(taz)x weberites (M = Fe, Co, Mn, Zn, Ga, V)

“…The spectra were recorded between 300 K and 77 K using both a bath cryostat and a homemade cryofurnace, in which the sample under helium atmosphere and secondary vacuum (10 -6 Torr), respectively, can be well thermalised (indeed, the instrumental design of the cryofurnace prevents from temperature deviations of the sample) [41][42][43][44][45][46] . In-field Mössbauer experiments were carried out using a cryomagnetic device where the applied field is oriented parallel to the -beam, the sample located in the main coil and the source in the compensated coil, preventing thus from polarization effects.…”

Magnetocaloric Behaviour in Amorphous and Nanocrystalline FeNbB Soft Magnetic Alloys

“…This material belongs to the group of the Fe-M-B-(Cu) alloys (M=Zr, Hf and Nb), called also NANOPERM. The particular interest in these alloys results from their excellent soft magnetic properties [3], which make them promising candidates for various soft magnetic applications. In spite of a large number of research activities on different aspects of magnetism in the NANOPERM alloys, they magnetocaloric properties remain fairly unexplored.…”

Nanocrystalline soft magnetic materials: intergrain coupling and spin freezing effects

“…Pieces of these ribbons were annealed under protective argon atmosphere for 1 hour at temperatures 743, 783 and 883 K in order to prepare the set of nanocrystalline samples characterized by different microstructure. A previous detailed structural characterization [10,11] has revealed that the sample annealed at 743 K for 1 hour represents an example of nanocrystalline system with a low fraction of bcc-Fe crystalline grains, the sample annealed at 783 K for 1 hour corresponds to the material in a medium stage of primary crystallization process and the sample annealed at 883 K for 1 hour represents a stage, where the primary crystallization process is nearly finished. The mean grain sizes that correspond to these different annealing stages are <8 nm, 10-14 nm and 15-20 nm, respectively.…”