MICROSTRUCTURAL EVOLUTION DURING HIGH ENERGY MECHANICAL MILLING AND HEAT TREATMENT OF Cu-(5,10)vol.%Al2O3 NANOCOMPOSITE POWDERS

Abstract

Cu -(5-10) vol .% Al 2 O 3 nanocomposite powders were produced from a mixture of Cu powder and Al 2 O 3 nanopowder using a high energy mechanical milling (HEMM) route consisting of two stages. The microstructural evolution of the Cu – Al 2 O 3 nanocomposite powder particles (or granules) produced after first and the second stages of milling was studied using scanning electron microscopy (SEM), transmission electron microcopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX) mapping. The study confirmed that homogenous dispersion of Al 2 O 3 nanoparticles in the Cu matrix was achieved after the first stage of milling and the relatively large Al 2 O 3 particles were further broken into smaller nanoparticles after the second stage of milling. The milled nanocomposite powders were also heat treated at 150, 300, 400 and 500°C for 1 hour, respectively, to determine the microstructural changes of the powder particles as a function of annealing temperature. It was found that after heat treatment at 150°C, the Cu grain sizes decreased due to recrystallisation, and increasing the annealing temperature to 300°C causes slight coarsening of the Cu grains. Further increasing the annealing temperature to 500°C caused significant coarsening of the Cu grains and the Al 2 O 3 nanoparticles. It also appeared that the coarsening of Cu grains in the composite powder particles after annealing at 500°C become less severe with increasing the volume fraction of Al 2 O 3 particles.