Limited quasicrystal formation in Zr-Ti-Cu-Ni-Al bulk metallic glasses

摘要

Bulk amorphous Zr_(62.x)Ti_xCu_(20)Ni_8Al_(10) alloys with compositions of 0 < = x < - 7.5 were prepared by copper mold casting. Thermal stability and crystallization behavior of the specimens were characterized by differential scanning calorimetry. Structures were studied by X-ray diffraction and transmission electron microscopy. The mass density of the as-cast samples and of selected annealed states was determined. The difference in density changes, between as-cast glassy, relaxed and crystallized structures, depends on the Ti content of the alloys. The higher the packing density of the glassy state, the higher is the thermal stability of the bulk glass due to a decrease in atomic mobility. Small gradations of Ti in steps of 0.2 at. percent reveal significant changes in the crystallization behavior of the alloys, concerning the size and the structure of the phases formed. Only compositions with 2 < = x < = 4 form a metastable quasicrystalline phase during the first transformation step.