The influence of the cooling rate on bulk metallic glass formation in Mg80Cu15Y5 and Mg80Cu10Y10

The Mg-Cu-Y system is known to be one of the best glass formers among the various existing magnesium alloys. The compositions chosen for the current study were Mg80Cu15Y5 and Mg80Cu10Y10. Different casting processes yielded four different microstructures that were analyzed by means of X-ray diffraction, scanning electron microscopy, high resolution scanning electron microscopy, and energy-dispersive X-ray spectroscopy chemical analysis. The different casting procedures were gravity castings of 3 mm diameter specimens into a copper mold held at different temperatures (cooled to -195 A degrees C with the aid of liquid nitrogen, held at room temperature and heated up to 300 A degrees C) and melt-spinning. Detailed microstructure study was then performed on the melt-spun specimen using transmission electron microscopy and high resolution transmission electron microscopy. The above-mentioned investigation revealed a crystalline rather than amorphous structure. The observed microstructure could not be explained on the basis of current models referring to the frequency of nucleation events.