Powder metallurgy of nanometric aluminium powders

摘要

The powder metallurgy processing (the compaction and the sintering) of aluminium nanocrystalline powder (with particle size of 100 nm) fabricated using a condensation process, has been studied. The compaction data were analysed using the Konopicky-Shapiro approach. This reveals that the particles are slightly harder than their coarse grained counterpart and that the powder densification is achieved by plastic flow of the nanoparticles. The sintering has been studied in vacuum and under hydrogen atmosphere and compared to the behaviour of a coarse particle powder (size 20 μm). The analysis, using the kinetic relations of sintering indicates that for nanoparticles, an initial stage of densification following a viscous flow mechanism occurs in the alumina hydroxide phase, located at the surface of the particles. Subsequently, the hydroxide is transformed into γ-alumina nanoparticles located at the aluminium grain boundaries. The sintering is then controlled by grain boundary diffusion coupled to aluminium plastic flow. The interpretations are supported by measurements of the activation energy and structural investigations using X-ray diffraction and transmission electron microscopy.