A microcrystalline Alni alloy with the nominal composition Fe51.1Ni23.5Al23.7Si1.7 was prepared by melt-spinning. Detailed studies of the spinodal decomposition (SD), microstructure and magnetic properties of the ribbons subjected to isothermal aging at Tag = 500-780 °C are reported. TEM investigations of the decomposition of the solid solution (β2 → β + β2) after melt-spinning and aging have revealed several types of decomposition products. As prepared melt spun ribbons show zone structure and antiphase domain (APD) boundaries inside grains. Aging at 500-600 °C led to the coarsening of the zone microstructure and to the appearance of discontinuous precipitates (DP) (β + β2 → β' + β'2) at grain boundaries. Aging at higher than 650 °C causes the formation of a modulated microstructure instead of a zone microstructure inside grains and coarsening of DP products. As prepared ribbons reveal soft magnetic properties (Hc = 480 Am-1). The maximum coercivity Hc = 20 kAm-1 was obtained for the ribbons aged at 700 °C. MFM method was used to image the magnetic microstructure of melt spun Alni ribbons subjected to aging.Keywords: Alni alloy, melt-spinning, aging, antiphase domains, discontinuous precipitates
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