Grain stabilisation of copper with nanoscaled Al2O3-powder

Copper powders with a median particle diameter of 60 μm were mixed with different amounts of nanosized alumina powder with a median particle diameter of 14 nm in an asymmetric moved mixer followed by hot extrusion. Investigations of the microstructure reveal considerable less recrystallization and grain growth up to temperatures near to the melting point of copper, compared to hot extruded samples made of copper powder without additives and composites with microsized alumina powder content. It was shown by EDX measurements, that the nanosized alumina particles are located exclusively at the grain boundaries of the copper grains. Due to the nanopowder additions an increase in hardness and yield stress is observed, which can be attributed to inhibited recrystallization and grain growth.