Precipitation of the icosahedral phase in amorphous Zr₆₅Cu_17.5-xAl_7.5Ni₁₀Ag_x (x=0, 2.5, 5, 7.5 and 10) alloys

An amorphous phase in Zr₆₅Al_7.5Cu_17.5Ni₁₀ crystallizes via co-precipitation of the I-phase and NiZr₂ phase in the first crystallization step, followed by decomposition of the I-phase into the CuZr₂ and NiZr₂ phases. The NiZr₂ phase transforms to a stable Zr₆NiAl₂ phase at a high temperature. The alloys containing Ag crystallize via a two-step process: firstly, the I-phase nucleates homogeneously and grows in an amorphous matrix; secondly, the quasicrystal and remaining amorphous phase transforms into the stable CuZr₂ and Zr₆NiAl₂ phases. With increasing Ag, the I-phase becomes more thermally stable and the grain size in the I-phase decreases due to increased frequency of homogeneous nucleation. The quasi-lattice constant of the I-phase decreases with increasing Ag content.