Fabrication and properties of mechanically milled alumina/aluminum nanocomposites

The reinforcement agglomeration in nanocomposites is a key issue that needs to be solved in order to fully benefit of the gain in strength and ductility associated with the decrease in reinforcement size from microscale to nanoscale. In this study, mechanical milling has been used successfully to disperse nanometric alumina (n-Al2O3) in an aluminum matrix. Al2O3/Al nanocomposite powders have been produced for various alumina sizes and concentrations. The 10 vol% n-Al2O3/Al powders display hardness values near five times higher than pure unmilled Al. A decrease in the Al2O3 particle size from 400 to 4 nm has increased the nanocomposite powder hardness by 11%. The microhardness and compression properties of an Al2O3/Al nanocomposite compact consolidated by hot pressing were measured. Comparison with modeled values and literature results indicates that the higher experimental yield strength obtained with the addition of n-Al2O3 versus micron size Al2O3 is due to in situ matrix strengthening.