Nanocrystallization-induced structural evolution of intergranular amorphous phase in Fe78B13Si9 alloy

The nanocrystallization-induced structural evolution of the intergranular amorphous phase in a Fe78B13Si9 alloy was investigated by X-ray diffraction (XRD) measurements, transmission electron microscopy (TEM), and positron annihilation spectroscopy. Crystallization occurs at 773 K, where nanocrystallites of α-Fe with an average grain size of a few tens of nanometers are formed in an amorphous matrix. With increasing annealing temperature up to 973 K, the average grain size increases up to ∼80 nm. In the as-prepared sample corresponding to an amorphous precursor, more than 90% of the positrons are localized at vacancy-sized free volumes dominantly surrounded by Fe atoms and other positrons are trapped by microvoids. Along with the appearance of nanocrystallites and their growth due to annealing, the concentration of microvoids is increased in the intergranular amorphous phase.