Mechanical–thermal synthesis of Al–Ce/Al2O3 nanocomposite powders

The aim of the present work is to produce aluminum matrix nanocomposite powders by displacement reaction between aluminum and ceria and to study the effect of high-energy ball milling on the onset temperature for the reduction reaction. If the onset temperature for the reduction reaction in the milled products during subsequent thermal treatment can be brought down below the melting temperature of the constituents, the reaction product can have very fine structure. This in turn accelerates the consolidation by lowering the sintering temperatures. Two different approaches, pure mechanosynthesis and combined mechanical and thermal synthesis, have been investigated to synthesize aluminum matrix nanocomposite powders by displacement reaction between aluminum and ceria. The ingredients have been subjected to high-energy ball milling up to 100 h in a planetary ball mill with hardened chrome steel grinding media. Differential thermal analysis, X-ray diffraction and electron microscopy have been used to study onset temperature for the reduction reaction and reaction mechanism. High-energy ball milling of the powder modifies the reactivity of the system and refinement of microstructure is accompanied by nanometer range crystallites and an increase in the lattice strain. The onset temperature for the displacement reaction has been reduced from 960 to 690 °C after 5 h of milling. An increase in the milling time up to 30 h changes the reaction to a solid-state reduction reaction. It has been shown that an appropriate combination of mechanical–thermal treatment may lead to the synthesis of aluminum-based nanocomposites by the solid-state processing.