Effect of mechanical milling on nanocrystalline grain stability and properties of Cu-Al2O3 composite prepared by thermo-chemical technique and hot extrusion

In this study, an influence of mechanical milling on the structural characteristics, mechanical properties and electrical conductivity of the ultrafine Cu-3 vol.% Al2O3 composite is analyzed. The initial Cu-Al2O3 powder was prepared by in situ thermo-chemical technique. Compared are two samples prepared by compacting of the non-milled and the intensively milled powder. The milling process ensured additional powder refinement and uniform distribution of secondary nano-particles in the Cu matrix. In the process of hot extrusion and annealing of the compact at elevated temperatures, the particles effectively strengthened crystallite/grain boundaries. Therefore, the composite has a homogeneous, thermal stable nanostructure up to 900 °C, good hardness of 130 HB and yield strength of 235 MPa. The composite prepared from the non-milled powder is characterized by a bimodal grain size microstructure, low hardness of 80 HB, lower yield strength of 185 MPa and it is structurally stable only up to 200 °C as a consequence of recrystallization processes and grain growth. The electrical conductivity of both materials is sufficient for electrotechnical applications.