A STUDY OF SOLID-STATE AMORPHIZATION IN ZR-30 AT-PERCENT AL BY MECHANICAL ATTRITION

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