Melting behavior of nanocrystalline aluminum powders

Abstract

Nanocrystalline aluminum powders have been synthesized by mechanical attrition under different atmospheres and by gas condensation. The crystal refinement and the development of the microstructure are investigated by x-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and electron energy loss spectrometry. Both preparation techniques lead to powders with comparable grain sizes. With decreasing grain size we find a drastic reduction of the melting point, ΔT_m, in comparison to the bulk value. Subsequent remelting does not recover the bulk melting point. The results are discussed in terms of the microstructure of the nanocrystalline powders, the contribution of the stored enthalphy of cold work, and the nucleation of disorder/melting at grain boundaries/particle interfaces.