Preparation of ultrafine and nanocrystalline FeAl powders

The increase in hardness or strength associated with decreasing grain size as predicted by the Hall-Petch effect points convincingly towards a need to produce ultrafine and nanocrystalline metallic and intermetallic powders. In this paper, we summarize our results obtained using a simple method based on pulsed laser vaporization followed by controlled condensation (LVCC) to synthesize nanometer sized metallic and intermetallic powders. Nanopowders of Fe. Al and intermetallic iron aluminide have been synthesized. Measurements of d-spacings from X-ray diffraction and electron diffraction confirm that the intermetallic nanopowders have the cubic FeAl (B2-CsCl) structure. The Population distribution as measured from the TEM images shows the average particle size for the FeAl nanoparticles is 6-10 nm. A thin amorphous coating is formed around the particles on exposure to air. The amorphous coating is found to be enriched in Al and oxygen as compared with the core of the particle when studied using nano-EDX and XPS measurements. Furthermore, by applying an electric field during the formation of the nanoparticles, it is possible to generate elongated fibers and tree-like assemblies of the aggregated nanoparticles. The potential applications of these materials are discussed. (C) 2002 Published by Elsevier Science B.V.