Formation and stability of bulk metallic glass forming Mg-Y-Cu alloys produced by mechanical alloying and rapid quenching

Mg55Y15Cu30 amorphous/nanocrystalline phase mixtures were prepared by mechanical alloying of elemental powders, rapid quenching, and ball milling of pieces of melt-spun ribbons. The samples were characterized by x-ray diffraction, constant-rate heating differential scanning calorimetry (DSC), isothermal annealing, and transmission electron microscopy (TEM). All samples exhibit a supercooled liquid region of more than 40 K before crystallization. Slight differences in the glass transition temperature T-g and rather significant changes in the crystallization temperature T-x were found for the samples prepared by the different techniques. The as-quenched ribbon shows a two-step crystallization behavior in contrast to the ball-milled ribbon and the mechanically alloyed powder which exhibit only one single crystallization step. Ball milling induces partial crystallization, suggesting that the microstructure of the ball-milled ribbon is very similar to that of the ribbon after the first crystallization step.