Ordering kinetics of disordered Ni 3Al synthesized by mechanical alloying

Abstract

The Ni[sub 3]Al compound belongs to that class of intermetallics whose virtual critical temperature for the order-disordered transformation is higher than the melting temperature. Chemically disordered Ni[sub 3]Al can be prepared by several methods including high energy ball milling (BM) of the ordered compound. Another possibility is offered by mechanical alloying (MA) of elemental Ni and Al powders. Aluminum and nickel powders in the 3:1 atomic ratio were mechanically alloyed in an air-cooled SPEX mill for times up to 40 hours. EDS microanalysis after MA showed an Fe contamination of about 2 and 4 at.% in the powders milled for 20 and 40 hours respectively. The structural characterization of the samples was performed by x-ray diffraction and their thermal stability was tested in a Perkin-Elmer DSC7 calorimeter. The diffraction patterns of the samples milled for at least 10 hours were very similar and showed the presence of a supersaturated fcc Ni(Al) solid solution whose diffraction peaks were considerably broadened with respect to those of the starting Ni powder.