Microstructure and properties of the in situ formed amorphous-crystalline composites in the Fe–Cu-based immiscible alloys

The paper presents microstructures and mechanical properties of the melt-spun Fe30Cu32Si13B9Al8Ni6Y2 and Fe44Cu18Si13B9Al8Ni6Y2 alloys. It was found that liquid phase separation of the initially homogeneous melt occurred due to a positive heat of mixing between two major elements. The microstructures of the melt-spun ribbons were composed of the Fe-rich amorphous and the Cu-rich crystalline phases. A significant effect of the melt ejection temperature and the chemical composition (Fe and Cu content) on microstructures of rapidly solidified alloys was revealed. The microstructures of ribbons melt-spun from the miscibility gap region were non-uniform. On the other hand the microstructures of ribbons melt-spun from homogeneous melt temperature region were composed of the spherical precipitates distributed within the matrix. Superior hardness values of the examined ribbons melt-spun from the same temperature were found for the alloy with higher iron content. An increase of the melt-ejection temperature in the homogeneous melt region resulted in hardness decrease in case of the Fe30Cu32Si13B9Al8Ni6Y2 alloy and its increase for the Fe44Cu18Si13B9Al8Ni6Y2 ribbons.

Research highlights
► Amorphous-crystalline microstructure of systems with a liquid miscibility gap.
► Fractal-like microstructure of the ribbons melt-spun from a homogeneous melt region.
► Decrease of volume fraction of precipitates with increasing melt ejection temperature.