Consolidation of ultrafine-grained Cu powder and nanostructured Cu–(2.5–10) vol%Al₂O₃ composite powders by powder compact forging

An as-received ultrafine-grained Cu powder and four nanostructured Cu–(2.5–10) vol%Al₂O₃ composite powders produced by high-energy mechanical milling of mixtures of the Cu powder and an Al₂O₃ nanopowder were consolidated using warm powder compaction followed by open die powder compact forging. The circular discs produced in the experiments achieved full densification. Tensile testing of the specimens cut from the forged discs showed that the Cu-forged disc had a fairly high yield strength of 330 MPa, UTS of 340 MPa and a plastic strain to fracture of 15%, but the Cu–Al₂O₃ composite-forged discs did not show any macroscopic plastic yielding. The fracture strength of the composite-forged discs decreased almost linearly with the increase of the volume fraction of Al₂O₃ nanoparticles. This study shows that a high level of consolidation of the ultrafine-grained Cu powder and the nanostructured Cu–2.5 vol%Al₂O₃ composite powder has been achieved by warm powder compacting at 350 °C and powder compact forging at 500 and 700 °C. However, this is not true for the nanostructured Cu–(5, 7.5 and 10) vol%Al₂O₃ composite powders, possibly due to their higher powder particle hardness at elevated temperatures in the range of 350–800 °C.