Precipitation of Icosahedral Phase in Zr-Ni-Nb-Cu-Al Metallic Glasses

Abstract

The crystallization behaviors of Zr-Ni-Nb-Cu-Al metallic glasses are greatly influenced by the substitution of Ni for Zr. For the glassy Zr71� xNixNb3Cu16Al10 (x ¼ 7, 9, 11 at%) alloys, the onset temperature of crystallization Tx increases from 717 to 748 K with increasing Ni content from 7 at% to 11 at%. The primary crystallization reaction of the studied glassy alloys corresponds to the formation of icosahedral phase from amorphous matrix. The precipitation of quasicrystalline phase with a large volume fraction in the Zr64Ni7Nb3Cu16Al10 alloy indicates that the decrease of Ni content promotes the formation of icosahedral phase. Johnson-Mehl-Avrami analysis of isothermal transformation data suggests that the icosahedral phase precipitation proceeds by a diffusion-controlled growth mode with nearly constant nucleation rate. Furthermore, the Zr71� xNixNb3Cu16Al10 (x ¼ 7, 9, 11 at%) alloys possess high glass-forming ability, and the critical diameter for glass formation reaching 6 mm, 9 mm and 9 mm by copper-mould casting method, respectively. [doi:10.2320/matertrans.M2009072]