Electron microscopy nanoscale characterization of ball milled Cu-Ag powders. Part II: Nanocomposites synthesized by elevated temperature milling or annealing

Microstructures and phases stabilized at steady state by variable temperature ball milling of Cu50Ag50 powders are characterized using transmission and scanning transmission electron microscopy. Starting from chemically mixed and cold-worked powders obtained by room temperature milling, it is shown that, upon increasing the milling temperature, the material first decomposes into Cu-rich and Ag-rich solid solutions, and then recrystallizes. A similar sequence is observed during the static annealing of the solid solution precursor. In both cases, Cu-Ag nanocomposites are synthesized, at a scale of a few nanometers in the unrecrystallized state, and at a scale ranging from 30 nm after dynamic recrystallization to 75 nm after static recrystallization. These nanocomposites exhibit high hardness values, approaching 6 GPa. Interestingly enough, recrystallization leads to an increase in the hardness of these materials. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.