FORMATION OF QUASICRYSTALLINE PHASE IN THE AORPHOUS MATRIX AND ITS EFFECT ON THE PLASTICITY IN ZR-TI-CU-NI-AL-NB BULK METALLIC GLASS SYSTEM

摘要

Several methods have been suggested recently to provide a global ductility to bulk metallic glasses (BMGs). In the most cases, in situ composites consisting of ductile crystalline and amorphous phases exhibit enhanced plastic elongation. The second crystalline phase distributed in the amorphous matrix may act as an initiation site of shear band resulting in multiple shear band formation throughout the specimen and confine the propagation of the shear bands. Recently, however, some as-cast monolithic BMGs have been reported to show increased plasticity. The reason for enhanced plasticity in monolithic BMGs is not clearly understood, yet. Park et al. insists that addition of element having positive heat of mixing enthalpy with constituent elements can be favorable to increase of ductility [1]. On the other hand, Park et al. have reported that the plasticity can be improved when quasicrystalline quenched-in nuclei exist in the amorphous matrix [2].