Kinetics of primary nanocrystallization in Al-rich metallic glass with quenched-in nuclei

The kinetics of primary nanocrystallization of an Al85Ni5Y8Co2 metallic glass, with quenched-in nuclei and a distinct glass transition temperature (Tg) upon heating, was studied by X-ray diffraction, differential scanning calorimetry, in situ electrical resistance measurement and high-resolution transmission electron microscopy. It was identified that a glass transition occurs before onset of primary crystallization reaction although quenched-in nuclei do exist in this glass. The formation and the evolution of the primary Al nanocrystals proceed at a separated mode: the growth of a few quenched-in nuclei of Al occurs predominantly well below Tg, followed by a high density nucleation in the residual amorphous matrix around Tg and finally growth of all nuclei developed before. This result provides a new insight into the microstructural control in Al-based metallic glasses.