Synthesis and structural analysis of aluminum nanocrystalline powders

The morphology and structure of aluminum nanocrystalline powders are studied using X-ray diffraction and high resolution electron microscopy. The powders are produced by a cryomelting process, based on spontaneous metal vapour condensation within a cryogenic medium. The as-produced powders are formed of free aluminum particles with 60% of them having a size less that 70 nm. Particles are covered by a 3 nm thick alumina layer whose structure depends on the aluminum surface orientation. The particles which interact during the synthesis undergo high plastic yielding with the formation of deformation twins, grain boundaries and the flattening of particles surfaces. (C) 1999 Acta Metallurgica Inc.