The Influence of Powder Particle Size on Properties of Cu-Al2O3 Composites

Inert gas atomized prealloyed copper powder containing 2 wt.% Al (average particle size approximate to 30 mu m) and a mixture consisting of copper (average particle sizes approximate to 15 mu m and 30 mu m) and 4 wt.% of commercial Al2O3 powder particles (average particle size approximate to 0.75 mu m) were milled separately in a high-energy planetary ball mill up to 20 h in air. Milling was performed in order to strengthen the copper matrix by grain size refinement and Al2O3 particles. Milling in air of prealloyed copper powder promoted formation of finely dispersed nano-sized Al2O3 particles by internal oxidation. On the other side, composite powders with commercial micro-sized Al2O3 particles were obtained by mechanical alloying. Following milling, powders were treated in hydrogen at 400 degrees C for 1h in order to eliminate copper oxides formed on their surface during milling. Hot pressing (800 degrees C for 3 h in argon at pressure of 35 MPa) was used for compaction of milled powders. Hot pressed composite compacts processed from 5 and 20 h milled powders were additionally subjected to high temperature exposure (800 degrees C for 1 and 5 h in argon) in order to examine their thermal stability. The results were discussed in terms of the effects of different size of starting powders, the grain size refinement and different size of Al2O3 particles on strengthening, thermal stability and electrical conductivity of copper-based composites.