Icosahedral quasicrystalline phase formation in Zr–Al–Ni–Cu glassy alloys by the addition of V, Nb and Ta

Abstract

The formation of an icosahedral quasicrystalline phase as a primary phase was found in Zr 65Al 7.5Ni 10Cu 12.5X 5 (X=V, Nb or Ta) glassy alloys. The icosahedral phase was precipitated during the first exothermic reaction in a two-stage crystallization process after a distinct glass transition. The diameters of the icosahedral particles are as small as 10–50 nm, similar to those found in Zr-based glassy alloys made with the addition of noble metals. Based on a Johnson–Mehl–Avrami analysis, we suggest that nano-quasicrystallization proceeds by a diffusion-controlled growth mode. The icosahedral phase in the Zr 65Al 7.5Ni 10Cu 17.5− x Ta x ( x=0–4) glassy alloys was formed at a Ta concentration of as little as 1 at.%, the primary crystallization phases were the fcc Zr 2Ni and icosahedral phases. For Ta concentrations above 3 at.%, a nearly single icosahedral phase was formed as the primary phase. The formation of a nano-scale icosahedral phase in Zr–Al–Ni–Cu glassy alloys with the addition of V, Nb or Ta, as well as noble metals, indicates that an increasing nucleation rate contributes to the precipitation of the icosahedral phase, leading to the concept that icosahedral short- or medium-range order exists in the glassy state of the Zr–Al–Ni–Cu alloy.