Properties of copper matrix reinforced with various size and amount of Al2O3 particles

Copper matrix was reinforced with Al2O3 particles of different size and amount by internal oxidation and mechanical alloying accomplished using high-energy ball milling in air. The inert gas-atomised prealloyed copper powder containing 1 wt.% Al as well as a mixture of electrolytic copper powder and 3 wt.% commercial Al2O3 powder served as starting materials. Milling of Cu-1 wt.% Al prealloyed powder promoted formation of fine dispersed particles (1.9 wt.% Al2O3, approximately 100 nm in size) by internal oxidation. During milling of Cu-3 wt.% Al2O3 powder mixture the uniform distribution of commercial Al2O3 particles has been obtained. Following milling, powders were treated in hydrogen at 400 °C for 1 h in order to eliminate copper oxides formed at the surface during milling. Compaction was executed by hot-pressing. Compacts processed from 5 to 20 h-milled powders were additionally subjected to high-temperature exposure at 800 °C in order to examine their thermal stability and electrical conductivity. Compacts of Cu-1 wt.% Al prealloyed powders with finer Al2O3 particles and smaller grain size exhibited higher microhardness than compacts of Cu-3 wt.% Al2O3 powder mixture. This indicates that nano-sized Al2O3 particles act as a stronger reinforcing parameter of the copper matrix than micro-sized commercial Al2O3 particles. Improved thermal stability of Cu-1 wt.% Al compacts compared to Cu-3 wt.% Al2O3 compacts implies that nano-sized Al2O3 particles act more efficiently as barriers obstructing grain growth than micro-sized particles. Contrary, the lower electrical conductivity of Cu-1 wt.% Al compacts is the result of higher electron scatter caused by nano-sized Al2O3 particles.