Ball milling-induced nanocrystal formation in aluminum-based metallic glasses

Abstract

Various experimental techniques have been used to investigate the effect of mechanical milling on the structural stability of rapidly solidified aluminum-based metallic glasses. Using transmission electron microscopy (TEM) and X-ray diffraction methods, the formation of nanocrystalline Al particles in some ball-milled Al-rich metallic glasses (such as Al 90 Fe 5 Gd 5 and Al 90 Fe 5 Ce 5 ) is clearly observed. For other compositions with lower Al concentration such as Al 85 Ni 5 Y 10 , no such phase transformation can be detected by TEM or X-ray. However, differential scanning calorimetry (DSC) measurements show that the crystallization peaks of the ball-milled Al 85 Ni 5 Y 10 metallic glass shifted to higher temperatures, while the crystallization enthalpy associated with the first exothermic peak decreased to a lower value, revealing that certain structural changes have taken place as a result of mechanical deformation. The compositional dependence of the structural stability of Al-based metallic glasses against mechanical deformation suggests that the nanocrystal formation induced by a deformation process is different from that caused by a thermal process. The large plastic strain induced atomic displacements and the enhancement of atomic mobility during the deformation process, are the possible mechanisms of mechanical deformation-induced crystallization. Our results demonstrate a new way of obtaining nanophase glassy composite alloy powders which are suitable for engineering applications upon further consolidation processing.