Lightweight, High-Strength, Age-Hardenable Nanoscale Materials

摘要

Phase transformations and precipitation behavior in age-hardenable nanoscale materials, using binary aluminum alloys as model materials, were studied. Nanoparticles of Al-Cu and Al-Zn were synthesized by a plasma ablation process. The particles (50-100 nm dia) were found to be supersaturated f.c.c. and were enveloped by a 2-4 nm amorphous Al oxide layer. On aging the Al-Cu nanoparticles, a precipitation sequence comprising nearly pure Cu precipitates to theta' to the equilibrium theta was observed, with all three forming along the Al oxide-matrix interface. In the Al-Zn nanoparticles, a spinodal structure was noted in the as-synthesized state, which evolved into a striated, f.c.c. twinned platelet structure within which were contained hcp precipitates also in twin relation; nearly pure Zn- precipitates also formed along the Al oxide- matrix interface. Ultra fine Al-Cu nanoparticles were also synthesized by inert gas condensation; these were found to be quite stable against precipitation during aging. Finally, the results revealed that Al nanopowders could be processed into bulk structures, leading to interesting Al-Al oxide nanocomposites with full densification and high hardness.