Properties of copper matrix reinforced with nano- and micro-sized Al2O3 particles

The mixture of electrolytic copper powder with 5 wt.% of commercial Al2O3 powder (average particle size: 15 and 0.75 μm, respectively) and the inert gas atomized prealloyed copper powder (average particle size: 30 μm) containing 2.5 wt.% aluminum were separately milled in air up to 20 h in the planetary ball mill. During milling aluminum in the prealloyed copper powders was oxidized in situ by internal oxidation with oxygen from the air forming very fine nano-sized Al2O3 particles. The internal oxidation of 2.5 wt.% aluminum generated 4.7 wt.% of Al2O3 in the copper matrix. Powders and compacts were characterized by light and scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction analysis. Microhardness and electrical conductivity were also included in measurements. The microhardness of Cu–2.5 wt.% Al compacts was 3.6 times higher than that of compacts processed from electrolytic copper powder. This increase in microhardness is a consequence of a fine dispersion of Al2O3 particles and refined grain structure. The average values of electrical conductivity of compacts processed from Cu–5 wt.% Al2O3 and Cu–2.5 wt.% Al powders previously milled for 20 h and were 88% and 70% IACS, respectively, which is a rather significant increase if compared with values of 60% and 23% IACS of compacts processed from as-received and non-milled powders. The microhardness of 20-h milled compacts decreases with the heat treatment at 800 °C. Due to the effect of nano-sized Al2O3 particles Cu–2.5 wt.% Al compacts show lower decrease in microhardness. The results are discussed in terms of the effect of Al2O3 particle size and fine grain structure on the reinforcing of the copper matrix.