Formation of nanocrystals in Zirconium-based alloys

Abstract

The formation of nanocrystals in Zr-based alloys through three different routes, viz by rapid solidification of alloys, by crystallization of rapidly solidified metallic glasses and by crystallization of bulk metallic glasses has been described. The nanocrystal forming behaviors of rapidly solidified metallic glasses and bulk metallic glasses have been compared and contrasted. The rapidly solidified alloys, which have been examined for this purpose, are Zr₇₆Fe_24-xNi_x (x = 0,4,8,12,16,24) and Zr_69.5Cu₁₂Ni₁₁Al_7.5. In the Zr_69.5Cu₁₂Ni₁₁Al_7.5 alloy, formation of a quasicrystalline phase was observed on crystallization. Bulk glass having the composition Zr₅₂Ti₆Al₁₀Cu₁₈Ni₁₄ has been produced by copper mould casting. This has been crystallized in order to obtain nanocrystalline phases having Zr₂Ni and Zr₂Cu structures. The nanocrystalline and the nanoquasicrystalline microstructures have been examined in considerable detail in order to find out the nature of the various types of interfaces in them. Particularly the nanograin boundaries were examined by high-resolution transmission electron microscope (HREM) and their structure has been compared with that of the grain boundary in large grained material. The change in nature of these interfaces and their number with coarsening of the nanocrystal is also investigated.