A study of solid-state amorphization in Zr-30 at. % Al by mechanical attrition

Abstract

Elemental powders of zirconium and aluminum in the atomic ratio of 70:30 were mechanically alloyed in an attritor under argon atmosphere using zirconia balls as milling media. Samples have been taken out for characterization after different durations of milling. The process of alloying and resultant amorphization had been studied using x-ray diffraction (XRD) and transmission electron microscopy (TEM). Scanning electron microscopy (SEM) was carried out to study the morphological changes occurring during repeated cold welding and breaking of the particles. Samples for TEM study were prepared by dispersing the mechanically attrited particles in the nickel foil by electrochemical codeposition. TEM study of the initial stages of milling revealed that localized structural changes precede the bulk amorphization process during mechanical alloying (MA). The sequence of phase evolution has been identified as (i) the formation of nanocrystalline supersaturated solid solution of aluminum in a-zirconium, (ii) amorphization of localized regions at powder interfaces, (iii) ordering of aluminum-rich regions in the metastable Zr₃Al (DO₁₉) phase, and, finally, (iv) bulk amorphization of the powders.