Synthesis and structural analysis of aluminum nanocrystalline powders

The morphology and structure of aluminum nanocrystalline powders are studie d using X-ray diffraction and high resolution electron microscopy. The powd ers are produced by a cryomelting process, based on spontaneous metal vapou r condensation within a cryogenic medium. The as-produced powders are forme d 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 depen ds on the aluminum surface orientation. The particles which interact during the synthesis undergo high plastic yielding with the formation of deformat ion twins, grain boundaries and the flattening of particles surfaces. (C) 1 999 Acta Metallurgica Inc.