Investigation of precipitation phases in as-cast wedge ingot of bulk amorphous Zr_56.6Cu_17.3Ni_12.5Al_9.6Ti₄ alloy

In order to clarify the competing relationships among the intermetallic precipitation phases during the cooling of a bulk amorphous Zr_56.6Cu_17.3Ni_12.5Al_9.6Ti₄ alloy, the wedge-shaped ingots of this alloy were made by casting the melt into a wedge-shaped copper mould, and then the zones with different cross-sections were studied by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that these phases are very different in both the morphology and sizes, and they are dependent on the thickness of wedge ingot, i.e., the cooling rates. It is therefore concluded that the Zr₂Ni phase is the strongest competing rival to the amorphous matrix in this alloy. These findings support that compared to Zr-Ni pair, Zr-Cu pair has a larger glass forming tendency. The glass forming ability can be improved by inhibiting the precipitation of Zr₂Ni phase by, for example, decreasing the Ni content in this alloy.